Turbo C/C++ and other junk compilers help, discussions and queries here

[The Incredible]

well ' LET US C++ ' by yaswant kanitkar

Let me know abt da publisher.

Anindya

 

[ashu888ashu888]

We r here to help u for ur exams buddy..dont worry....we all will help u as ur exams r near and we understand ur situation..so dont panic..

cheers n e-peace...

 

[The Incredible]

Thanks ashu888ahsu888 for that kinda reply.

thanks a lot.


Anindya

 

[ashu888ashu888]

Always Incredible..

U can hv all ur posts covered in this thread and we wil help u in wat ever way we can....I know the pressures of exam buddy...but did all the previous codes workd on ur compiler>?>

cheers n e-peace...

 

[The Incredible]

Thanks!

No. I've only saved 'em in cpp format. sum of da progs i've ran. n they worked but i'm having confusion with compound interrest prog.

i entered

P = 100

I = 10

T = 2

then i got

CI = 121

but accord 2 me, it shud b 11


BTW if u know abt da rest 2 progs plz let me know.


Anindya

 

[ashu888ashu888]

According to me..in Compound interest,the Amount (Principle+Interest) of the first year becomes the Principle for the second year (im not sure abt the funda thou.. ) and so on..so maybe u can use this funda and use it in the program...

That it: Amount=(P*N*R)/100 and this Amount will become the Principle for the 2nd year and so on.....

But its better to understand the concept of all these programs rather than MUGGING all up coz then u will forget everything buddy....so jus make sure that u understand the program...its concepts..and then apply ur codes..

cheers n e-peace....

 

[The Incredible]

well i know da pricipal changes every year but man i've asked for ci not p

ci of next year shud b 11


BTW i know that i need to understand basic concepts that's why i've asked plz provide codes with header files n basic concepts n logics.


BTW wat's algorithm. my eng is a bit bad.

PS: if any1 having codes of da rest 2 progs plz gimme.


Anindya

 

[anubhav_har]

Which codes do you need now.. and the compound intrerest problem I mentioned was working fine.. check again..

 

[anubhav_har]

Hey man compund interest is amount - principle... amount formula is P[(1+(R/100))^n] therefore there are changes in the code i gave

#include<iostream.h>
#include<conio.h>
#include<math.h>
void main()
{
clrscr();
float p,r,n,ci,amount;
cout<<"\nEnter principal:";
cin>>p;
cout<<"\nEnter rate:";
cin>>r;
cout<<"\nEnter time:";
cin>>n;
amount=p*pow((1+(r/100)),n);
ci=amount-p;
cout<<"\nThe compound interest is: "<<ci;
getch();
}

Quadratic eqn program

#include<iostream.h>
#include<conio.h>
#include<math.h>
void main()
{
clrscr();
float a,b,c,d,sqrtd,r1,r2;
cout<<"\nEnter values of a,b,and c for equation ax^2+bx+c:";
cin>>a>>b>>c;
d=(b*b)-(4*a*c);
sqrtd=sqrt(d);
r1=(-b+sqrtd)/(2*a);
r2=(-b-sqrtd)/(2*a);
cout<<"\nThe roots are: "<<r1<<","<<r2;
getch();
}

 

[The Incredible]

Hey!

Thanks a lotta!

in ur formula u wrote ^N

but in coed u rote ,N

also wat does pow stands for?



PS: if any1 last program , plz let me know.

Anindya

 

[mach]

Hey Incredible.. as it seems u have some time to spend around on this forum..

here 's a c++ primer for you.. this can get u thru some of the basic stuff that u ought to know be4 giving a c++ written/practical/oral exam
Hope this helps you to some extent
The content on c++ i am providing is from this site

*www.cprogramming.com/tutorial.html

 Lesson 1

C++ is a programming language of many different dialects, similar to the way that each spoken language has many different dialects. In C++, dialects are not because the speakers live in the North or South. Instead, it is because there are many different compilers that support slightly different features. There are several common compilers: in particular, Borland C++, Microsoft C++, and GNU C++. There are also many front-end environments for the different compilers--the most common is Dev-C++ around GNU's G++ compiler. Some, such as G++, are free, while others are not. Please see the compiler listing for more information on how to get a compiler and set it up.

Each of these compilers is slightly different. Each one should support the ANSI/ISO standard C++ functions, but each compiler will also have nonstandard functions (these functions are similar to slang spoken in different parts of a country). Sometimes the use of nonstandard functions will cause problems when you attempt to compile source code (the actual C++ written by a programmer and saved as a text file) with a different compiler. These tutorials use ANSI/ISO standard C++ and should not suffer from this problem (with sufficiently modern compilers). Note that if you are using an older compiler, such as TCLite, you should read check out some compatability issues.

If you don't have a compiler, I strongly suggest that you get one. A simple compiler is sufficient for our use, but make sure that you do get one in order to get the most from these tutorials. The page linked above, compilers, lists compilers by operating system.

C++ is a different breed of programming language. A C++ program begins with a function, a collection of commands that do "something". The function that begins a C++ program is called main; this function is always called when the program first executes. From main, we can also call other functions whether they be written by us or by others. To access a standard function that comes with the compiler, you include a header with the #include directive. What this does is effectively take everything in the header and paste it into your program. Let's look at a working program:

#include <iostream>

using namespace std;

int main()
{
  cout<<"HEY, you, I'm alive! Oh, and Hello World!\n";
  cin.get();
}

Let's look at the elements of the program. The #include is a "preprocessor" directive that tells the compiler to put code from the header called iostream into our program before actually creating the executable. By including header files, you an gain access to many different functions. For example, the cout function requires iostream. Following the include is the statement, "using namespace std;". This line tells the compiler to use a group of functions that are part of the standard library (std). By including this line at the top of a file, you allow the program to use functions such as cout. The semicolon is part of the syntax of C and C++. It tells the compiler that you're at the end of a command. You will see later that the semicolon is used to end most commands in C++.

The next imporant line is int main(). This line tells the compiler that there is a function named main, and that the function returns an integer, hence int. The "curly braces" ({ and }) signal the beginning and end of functions and other code blocks. If you have programmed in Pascal, you will know them as BEGIN and END. Even if you haven't programmed in Pascal, this is a good way to think about their meaning.

The next line of the program may seem strange. If you have programmed in another language, you might expect that print would be the function used to display text. In C++, however, the cout object is used to display text. It uses the << symbols, known as "insertion operators", to indicate what to output. cout<< results in a function call with the ensuing text as an argument to the function. The quotes tell the compiler that you want to output the literal string as-is. The '\n' sequence is actually treated as a single character that stands for a newline (we'll talk about this later in more detail). It moves the cursor on your screen to the next line. Again, notice the semicolon: it is added onto the end of all, such as function calls, in C++.

The next command is cin.get(). This is another function call: it reads in input and expects the user to hit the return key. Many compiler environments will open a new console window, run the program, and then close the window. This command keeps that window from closing because the program is not done yet because it waits for you to hit enter. Including that line gives you time to see the program run.

Upon reaching the end of main, the closing brace, our program will return the value of 0 (and integer, hence why we told main to return an int) to the operating system. This return value is important as it can be used to tell the OS whether our program succeeded or not. A return value of 0 means success and is returned automatically (but only for main, other functions require you to manually return a value), but if we wanted to return something else, such as 1, we would have to do it with a return statement:

#include <iostream>

using namespace std;

int main()
{
  cout<<"HEY, you, I'm alive! Oh, and Hello World!\n";
  cin.get();

  return 1;
}

The final brace closes off the function. You should try compiling this program and running it. You can cut and paste the code into a file, save it as a .cpp (or whatever extension your compiler requires) file. If you are using a command-line compiler, such as Borland C++ 5.5, you should read the compiler instructions for information on how to compile. Otherwise compiling and running should be as simple as clicking a button with your mouse.

You might start playing around with the cout function and get used to writing C++.

Comments are critical for all but the most trivial programs and this tutorial will often use them to explain sections of code. When you tell the compiler a section of text is a comment, it will ignore it when running the code, allowing you to use any text you want to describe the real code. To create a comment use either //, which tells the compiler that the rest of the line is a comment, or /* and then */ to block off everything between as a comment. Certain compiler environments will change the color of a commented area, but some will not. Be certain not to accidentally comment out code (that is, to tell the compiler part of your code is a comment) you need for the program. When you are learning to program, it is useful to be able to comment out sections of code in order to see how the output is affected.

So far you should be able to write a simple program to display information typed in by you, the programmer and to describe your program with comments. That's great, but what about interacting with your user? Fortunately, it is also possible for your program to accept input. The function you use is known as cin, and is followed by the insertion operator >>.

Of course, before you try to receive input, you must have a place to store that input. In programming, input and data are stored in variables. There are several different types of variables; when you tell the compiler you are declaring a variable, you must include the data type along with the name of the variable. Several basic types include char, int, and float.

A variable of type char stores a single character, variables of type int store integers (numbers without decimal places), and variables of type float store numbers with decimal places. Each of these variable types - char, int, and float - is each a keyword that you use when you declare a variable.

Sometimes it can be confusing to have multiple variable types when it seems like some variable types are redundant. Using the right variable size can be important for making your code readable and for efficiency--some variables require more memory than others. For now, suffice it to say that the different variable types will almost all be used!

To declare a variable you use the syntax type <name>. It is permissible to declare multiple variables of the same type on the same line; each one should be separated by a comma. The declaration of a variable or set of variables should be followed by a semicolon (Note that this is the same procedure used when you call a function). If you attempt to use an undefined variable, your program will not run, and you will receive an error message informing you that you have made a mistake.

Here are some variable declaration examples: 
 
int x;
int a, b, c, d;
char letter;
float the_float;

While you can have multiple variables of the same type, you cannot have multiple variables with the same name. Moreover, you cannot have variables and functions with the same name.

Here is a sample program demonstrating the use a a variable: 
 
#include <iostream>

using namespace std;

int main()
{
  int thisisanumber;

  cout<<"Please enter a number: ";
  cin>> thisisanumber;
  cin.ignore();
  cout<<"You entered: "<< thisisanumber <<"\n";
  cin.get();
}

Let's break apart this program and examine it line by line. The keyword int declares thisisanumber to be an integer. The function cin>> reads a value into thisisanumber; the user must press enter before the number is read by the program. cin.ignore() is another function that reads and discards a character. Remember that when you type intput into a program, it takes the enter key too. We don't need this, so we throw it away. Keep in mind that the variable was declared an integer; if the user attempts to type in a decimal number, it will be truncated (that is, the decimal component of the number will be ignored). Try typing in a sequence of characters or a decimal number when you run the example program; the response will vary from input to input, but in no case is it particularly pretty. Notice that when printing out a variable quotation marks are not used. Were there quotation marks, the output would be "You Entered: thisisanumber." The lack of quotation marks informs the compiler that there is a variable, and therefore that the program should check the value of the variable in order to replace the variable name with the variable when executing the output function. Do not be confused by the inclusion of two separate insertion operators on one line. Including multiple insertion operators on one line is perfectly acceptable and all of the output will go to the same place. In fact, you must separate string literals (strings enclosed in quotation marks) and variables by giving each its own insertion operators (<<). Trying to put two variables together with only one << will give you an error message, do not try it. Do not forget to end functions and declarations with a semicolon. If you forget the semicolon, the compiler will give you an error message when you attempt to compile the program.

Of course, no matter what type you use, variables are uninteresting without the ability to modify them. Several operators used with variables include the following: *, -, +, /, =, ==, >, <. The * multiplies, the - subtracts, and the + adds. It is of course important to realize that to modify the value of a variable inside the program it is rather important to use the equal sign. In some languages, the equal sign compares the value of the left and right values, but in C++ == is used for that task. The equal sign is still extremely useful. It sets the left input to the equal sign, which must be one, and only one, variable equal to the value on the right side of the equal sign. The operators that perform mathematical functions should be used on the right side of an equal sign in order to assign the result to a variable on the left side.

Here are a few examples: 
 
a = 4 * 6; // (Note use of comments and of semicolon) a is 24
a = a + 5; // a equals the original value of a with five added to it
a == 5     // Does NOT assign five to a. Rather, it checks to see if a equals 5

.

The other form of equal, ==, is not a way to assign a value to a variable. Rather, it checks to see if the variables are equal. It is useful in other areas of C++; for example, you will often use == in such constructions as conditional statements and loops. You can probably guess how < and > function. They are greater than and less than operators.

For example: 
 
a < 5  // Checks to see if a is less than five
a > 5  // Checks to see if a is greater than five
a == 5 // Checks to see if a equals five, for good measure

 

[mach]

Lesson 2: If statements

The ability to control the flow of your program, letting it make decisions on what code to execute, is valuable to the programmer. The if statement allows you to control if a program enters a section of code or not based on whether a given condition is true or false. One of the important functions of the if statement is that it allows the program to select an action based upon the user's input. For example, by using an if statement to check a user entered password, your program can decide whether a user is allowed access to the program.

Without a conditional statement such as the if statement, programs would run almost the exact same way every time. If statements allow the flow of the program to be changed, and so they allow algorithms and more interesting code.

Before discussing the actual structure of the if statement, let us examine the meaning of TRUE and FALSE in computer terminology. A true statement is one that evaluates to a nonzero number. A false statement evaluates to zero. When you perform comparison with the relational operators, the operator will return 1 if the comparison is true, or 0 if the comparison is false. For example, the check 0 == 2 evaluates to 0. The check 2 == 2 evaluates to a 1. If this confuses you, try to use a cout statement to output the result of those various comparisons (for example cout<< ( 2 == 1 )

When programming, the aim of the program will often require the checking of one value stored by a variable against another value to determine whether one is larger, smaller, or equal to the other.

There are a number of operators that allow these checks.

Here are the relational operators, as they are known, along with examples: 
 
>     greater than              5 > 4 is TRUE
<     less than                 4 < 5 is TRUE
>=    greater than or equal     4 >= 4 is TRUE
<=    less than or equal        3 <= 4 is TRUE
==    equal to                  5 == 5 is TRUE
!=    not equal to              5 != 4 is TRUE

It is highly probable that you have seen these before, probably with slightly different symbols. They should not present any hindrance to understanding. Now that you understand TRUE and FALSE in computer terminology as well as the comparison operators, let us look at the actual structure of if statements.

The structure of an if statement is as follows: 
 
if ( TRUE )
  Execute the next statement

To have more than one statement execute after an if statement that evaluates to true, use braces, like we did with the body of a function. Anything inside braces is called a compound statement, or a block.

For example: 
 
if ( TRUE ) {
  Execute all statements inside the braces
}

There is also the else statement. The code after it (whether a single line or code between brackets) is executed if the if statement is FALSE.

It can look like this:

if ( TRUE ) {
  // Execute these statements if TRUE
}
else {
  // Execute these statements if FALSE
}

One use for else is if there are two conditional statements that may both evaluate to true, yet you wish only one of the two to have the code block following it to be executed. You can use an else if after the if statement; that way, if the first statement is true, the else if will be ignored, but if the if statement is false, it will then check the condition for the else if statement. If the if statement was true the else statement will not be checked. It is possible to use numerous else if statements.

Let's look at a simple program for you to try out on your own.

#include <iostream>	

using namespace std;
		
int main()                            // Most important part of the program!
{
  int age;                            // Need a variable...
  
  cout<<"Please input your age: ";    // Asks for age
  cin>> age;                          // The input is put in age
  cin.ignore();                       // Throw away enter
  if ( age < 100 ) {                  // If the age is less than 100
     cout<<"You are pretty young!\n"; // Just to show you it works...
  }
  else if ( age == 100 ) {            // I use else just to show an example 
     cout<<"You are old\n";           // Just to show you it works...
  }
  else {
    cout<<"You are really old\n";     // Executed if no other statement is
  }
  cin.get();
}

Boolean operators allow you to create more complex conditional statements. For example, if you wish to check if a variable is both greater than five and less than ten, you could use the boolean AND to ensure both var > 5 and var < 10 are true. In the following discussion of boolean operators, I will capitalize the boolean operators in order to distinguish them from normal english. The actual C++ operators of equivalent function will be described further into the tutorial - the C++ symbols are not: OR, AND, NOT, although they are of equivalent function.

When using if statements, you will often wish to check multiple different conditions. You must understand the Boolean operators OR, NOT, and AND. The boolean operators function in a similar way to the comparison operators: each returns 0 if evaluates to FALSE or 1 if it evaluates to TRUE.

NOT: The NOT operator accepts one input. If that input is TRUE, it returns FALSE, and if that input is FALSE, it returns TRUE. For example, NOT (1) evalutes to 0, and NOT (0) evalutes to 1. NOT (any number but zero) evaluates to 0. In C and C++ NOT is written as !. NOT is evaluated prior to both AND and OR.

AND: This is another important command. AND returns TRUE if both inputs are TRUE (if 'this' AND 'that' are true). (1) AND (0) would evaluate to zero because one of the inputs is false (both must be TRUE for it to evaluate to TRUE). (1) AND (1) evaluates to 1. (any number but 0) AND (0) evaluates to 0. The AND operator is written && in C++. Do not be confused by thinking it checks equality between numbers: it does not. Keep in mind that the AND operator is evaluated before the OR operator.

OR: Very useful is the OR statement! If either (or both) of the two values it checks are TRUE then it returns TRUE. For example, (1) OR (0) evaluates to 1. (0) OR (0) evaluates to 0. The OR is written as || in C++. Those are the pipe characters. On your keyboard, they may look like a stretched colon. On my computer the pipe shares its key with \. Keep in mind that OR will be evaluated after AND.

It is possible to combine several boolean operators in a single statement; often you will find doing so to be of great value when creating complex expressions for if statements. What is !(1 && 0)? Of course, it would be TRUE. It is true is because 1 && 0 evaluates to 0 and !0 evaluates to TRUE (ie, 1).

Try these statements for urself

A. !( 1 || 0 )         ANSWER: 0	
B. !( 1 || 1 && 0 )    ANSWER: 0 (AND is evaluated before OR)
C. !( ( 1 || 0 ) && 0 )  ANSWER: 1 (Parenthesis are useful)

 

[mach]

Lesson 3: Loops

Loops are used to repeat a block of code. Being able to have your program repeatedly execute a block of code is one of the most basic but useful tasks in programming -- many programs or websites that produce extremely complex output (such as a message board) are really only executing a single task many times. (They may be executing a small number of tasks, but in principle, to produce a list of messages only requires repeating the operation of reading in some data and displaying it.) Now, think about what this means: a loop lets you write a very simple statement to produce a significantly greater result simply by repetition.

One Caveat: before going further, you should understand the concept of C++'s true and false, because it will be necessary when working with loops (the conditions are the same as with if statements). There are three types of loops: for, while, and do..while. Each of them has their specific uses. They are all outlined below.

FOR - for loops are the most useful type. The syntax for a for loop is

for ( variable initialization; condition; variable update ) {
  Code to execute while the condition is true
}

The variable initialization allows you to either declare a variable and give it a value or give a value to an already existing variable. Second, the condition tells the program that while the conditional expression is true the loop should continue to repeat itself. The variable update section is the easiest way for a for loop to handle changing of the variable. It is possible to do things like x++, x = x + 10, or even x = random ( 5 ), and if you really wanted to, you could call other functions that do nothing to the variable but still have a useful effect on the code. Notice that a semicolon separates each of these sections, that is important. Also note that every single one of the sections may be empty, though the semicolons still have to be there. If the condition is empty, it is evaluated as true and the loop will repeat until something else stops it.

Example: 
 
#include <iostream>

using namespace std; // So the program can see cout and endl

int main()
{
  // The loop goes while x < 10, and x increases by one every loop
  for ( int x = 0; x < 10; x++ ) {
    // Keep in mind that the loop condition checks 
    //  the conditional statement before it loops again.
    //  consequently, when x equals 10 the loop breaks.
    // x is updated before the condition is checked.    
    cout<< x <<endl;
  }
  cin.get();
}

This program is a very simple example of a for loop. x is set to zero, while x is less than 10 it calls cout<< x <<endl; and it adds 1 to x until the condition is met. Keep in mind also that the variable is incremented after the code in the loop is run for the first time.

WHILE - WHILE loops are very simple. The basic structure is

while ( condition ) { Code to execute while the condition is true }

The true represents a boolean expression which could be x == 1 or while ( x != 7 ) (x does not equal 7). It can be any combination of boolean statements that are legal. Even, (while x ==5 || v == 7) which says execute the code while x equals five or while v equals 7. Notice that a while loop is the same as a for loop without the initialization and update sections. However, an empty condition is not legal for a while loop as it is with a for loop.

Example: 
 
#include <iostream>

using namespace std; // So we can see cout and endl

int main()
{ 
  int x = 0;  // Don't forget to declare variables
  
  while ( x < 10 ) { // While x is less than 10 
    cout<< x <<endl;
    x++;             // Update x so the condition can be met eventually
  }
  cin.get();
}

This was another simple example, but it is longer than the above FOR loop. The easiest way to think of the loop is that when it reaches the brace at the end it jumps back up to the beginning of the loop, which checks the condition again and decides whether to repeat the block another time, or stop and move to the next statement after the block.

DO..WHILE - DO..WHILE loops are useful for things that want to loop at least once. The structure is

do {
} while ( condition );

Notice that the condition is tested at the end of the block instead of the beginning, so the block will be executed at least once. If the condition is true, we jump back to the beginning of the block and execute it again. A do..while loop is basically a reversed while loop. A while loop says "Loop while the condition is true, and execute this block of code", a do..while loop says "Execute this block of code, and loop while the condition is true".

Example: 
 
#include <iostream>

using namespace std;

int main()
{
  int x;

  x = 0;
  do {
    // "Hello, world!" is printed at least one time
    //  even though the condition is false
    cout<<"Hello, world!\n";
  } while ( x != 0 );
  cin.get();
}

Keep in mind that you must include a trailing semi-colon after the while in the above example. A common error is to forget that a do..while loop must be terminated with a semicolon (the other loops should not be terminated with a semicolon, adding to the confusion). Notice that this loop will execute once, because it automatically executes before checking the condition.

 

[ashu888ashu888]

Hey Mach bro ! Mr.Incredible already said tat he didnt get any help from the site that u mentioned..

 

[mach]

Lesson 4: Functions

Now that you should have learned about variables, loops, and conditional statements it is time to learn about functions. You should have an idea of their uses as we have already used them and defined one in the guise of main. cin.get() is an example of a function. In general, functions are blocks of code that perform a number of pre-defined commands to accomplish something productive.

Functions that a programmer writes will generally require a prototype. Just like a blueprint, the prototype tells the compiler what the function will return, what the function will be called, as well as what arguments the function can be passed. When I say that the function returns a value, I mean that the function can be used in the same manner as a variable would be. For example, a variable can be set equal to a function that returns a value between zero and four.

For example: 
 
#include <cstdlib>   // Include rand()

using namespace std; // Make rand() visible

int a = rand(); // rand is a standard function that all compilers have

Do not think that 'a' will change at random, it will be set to the value returned when the function is called, but it will not change again.

The general format for a prototype is simple: 
 
return-type function_name ( arg_type arg1, ..., arg_type argN );

arg_type just means the type for each argument -- for instance, an int, a float, or a char. It's exactly the same thing as what you would put if you were declaring a variable.

There can be more than one argument passed to a function or none at all (where the parentheses are empty), and it does not have to return a value. Functions that do not return values have a return type of void. Lets look at a function prototype:

int mult ( int x, int y );

This prototype specifies that the function mult will accept two arguments, both integers, and that it will return an integer. Do not forget the trailing semi-colon. Without it, the compiler will probably think that you are trying to write the actual definition of the function.

When the programmer actually defines the function, it will begin with the prototype, minus the semi-colon. Then there should always be a block with the code that the function is to execute, just as you would write it for the main function. Any of the arguments passed to the function can be used as if they were declared in the block. Finally, end it all with a cherry and a closing brace. Okay, maybe not a cherry.

Lets look at an example program: 
 
#include <iostream>

using namespace std;

int mult ( int x, int y );

int main()
{
  int x;
  int y;
  
  cout<<"Please input two numbers to be multiplied: ";
  cin>> x >> y;
  cin.ignore();
  cout<<"The product of your two numbers is "<< mult ( x, y ) <<"\n";
  cin.get();
}

int mult ( int x, int y )
{
  return x * y;
}

This program begins with the only necessary include file and a directive to make the std namespace visible. Everything in the standard headers is inside of the std namespace and not visible to our programs unless we make them so. Next is the prototype of the function. Notice that it has the final semi-colon! The main function returns an integer, which you should always have to conform to the standard. You should not have trouble understanding the input and output functions. It is fine to use cin to input to variables as the program does. But when typing in the numbers, be sure to separate them by a space so that cin can tell them apart and put them in the right variables.

Notice how cout actually outputs what appears to be the mult function. What is really happening is cout is printing the value returned by mult, not mult itself. The result would be the same as if we had use this print instead

cout<<"The product of your two numbers is "<< x * y <<"\n";

The mult function is actually defined below main. Due to its prototype being above main, the compiler still recognizes it as being defined, and so the compiler will not give an error about mult being undefined. As long as the prototype is present, a function can be used even if there is no definition. However, the code cannot be run without a definition even though it will compile. The prototype and definition can be combined into one also. If mult were defined before it is used, we could do away with the prototype because the definition can act as a prototype as well.

Return is the keyword used to force the function to return a value. Note that it is possible to have a function that returns no value. If a function returns void, the retun statement is valid, but only if it does not have an expression. In otherwords, for a function that returns void, the statement "return;" is legal, but redundant.

The most important functional (Pun semi-intended) question is why do we need a function? Functions have many uses. For example, a programmer may have a block of code that he has repeated forty times throughout the program. A function to execute that code would save a great deal of space, and it would also make the program more readable. Also, having only one copy of the code makes it easier to make changes. Would you rather make forty little changes scattered all throughout a potentially large program, or one change to the function body? So would I.

Another reason for functions is to break down a complex program into logical parts. For example, take a menu program that runs complex code when a menu choice is selected. The program would probably best be served by making functions for each of the actual menu choices, and then breaking down the complex tasks into smaller, more manageable tasks, which could be in their own functions. In this way, a program can be designed that makes sense when read. And has a structure that is easier to understand quickly. The worst programs usually only have the required function, main, and fill it with pages of jumbled code.

 

[mach]

Lesson 5: switch case

Switch case statements are a substitute for long if statements that compare a variable to several "integral" values ("integral" values are simply values that can be expressed as an integer, such as the value of a char). The basic format for using switch case is outlined below. The value of the variable given into switch is compared to the value following each of the cases, and when one value matches the value of the variable, the computer continues executing the program from that point.

switch ( <variable> ) {
case this-value:
  Code to execute if <variable> == this-value
  break;
case that-value:
  Code to execute if <variable> == that-value
  break;
...
default:
  Code to execute if <variable> does not equal the value following any of the cases
  break;
}

The condition of a switch statement is a value. The case says that if it has the value of whatever is after that case then do whatever follows the colon. The break is used to break out of the case statements. Break is a keyword that breaks out of the code block, usually surrounded by braces, which it is in. In this case, break prevents the program from falling through and executing the code in all the other case statements. An important thing to note about the switch statement is that the case values may only be constant integral expressions. Sadly, it isn't legal to use case like this:

int a = 10;
int b = 10;
int c = 20;

switch ( a ) {
case b:
  // Code
  break;
case c:
  // Code
  break;
default:
  // Code
  break;
}

The default case is optional, but it is wise to include it as it handles any unexpected cases. Switch statements serves as a simple way to write long if statements when the requirements are met. Often it can be used to process input from a user.

Below is a sample program, in which not all of the proper functions are actually declared, but which shows how one would use switch in a program.

#include <iostream>

using namespace std;

void playgame();
void loadgame();
void playmultiplayer();
	
int main()
{
  int input;
  
  cout<<"1. Play game\n";
  cout<<"2. Load game\n";
  cout<<"3. Play multiplayer\n";
  cout<<"4. Exit\n";
  cout<<"Selection: ";
  cin>> input;
  switch ( input ) {
  case 1:            // Note the colon, not a semicolon
    playgame();
    break;
  case 2:            // Note the colon, not a semicolon
    loadgame();
    break;
  case 3:            // Note the colon, not a semicolon
    playmultiplayer();
    break;
  case 4:            // Note the colon, not a semicolon
    cout<<"Thank you for playing!\n";
    break;
  default:            // Note the colon, not a semicolon
    cout<<"Error, bad input, quitting\n";
    break;
  }
  cin.get();
}

This program will compile, but cannot be run until the undefined functions are given bodies, but it serves as a model (albeit simple) for processing input. If you do not understand this then try mentally putting in if statements for the case statements. Default simply skips out of the switch case construction and allows the program to terminate naturally. If you do not like that, then you can make a loop around the whole thing to have it wait for valid input. You could easily make a few small functions if you wish to test the code.

 

[mach]

Hey Mach bro ! Mr.Incredible already said tat he didnt get any help from the site that u mentioned..

Hi ashu bro..
i havnt yet mentioned a site be4 i posted the tutz.. and i also dont see where mr incredible say he didnt find it useful

he only mentioned that he had no time to search/read books ..
but as i see he is a regualr to the forum even during his exams are so close.. i thnk he and some others mght find this simple tutorial interesting

for a comp exam if it is written.. u ned to know the basic concepts..
even for a practical exam.. basic concepts are somethng that need to be known..same is required if any viva/questions are asked regarding his program
like y he used a loop, why he used if..else control statement and y not while.. switch.. these are basic concepts

its true his exams are near.. but he isnt going to score nythng unless he knows some of the basic stuff.. who knows if he will be asked the same questions he has listed here.. he needs to understand the concepts to some extent

he says he has no time for comp studies.. yet its still on 30.. he has some time.. it wont take more than 30 minutes to read what i have posted and abt 1-2 hrs more to try the codes posted..

if he can spend time on an online forum be4 exams.. i am sure he wont mind spending some time reading the simple tutorial posted especially for him on the forum

these are the simplest tutz i could find when i had started with c++ and so am sharing them.. hope this helps u mr incredible.. and soem others as well...

@ Mr Incredible.. if u have other concepts like function, arrays, structures.. u can spend some time on the site i mentioned atleast ur concepts will be clear to some extent

when i posted the tutz i had in mind that someone else besides mr incredible will also find them useful..

I mean no offense to nyone ..

 

[anubhav_har]

C'mon Guys!

i'm not having time to read da buks n uderstand da logics.

i've already mentioned that my compu exams r on 30th.

man do u all want that i shud only concentrate on comp. man this is cbse board i hav other subjects too. this yr only joined this school.

n abt gaining knowledge let me tel u there's a institute around 2 km from my house for learning programming languages such as BASIC C++ COBOL and JAVA. but currently i'm not having time to read n understand them. from 20th my exams r beginning.

also, in case of reading e-buks electricity needs to b there. if u don't trust just join my city nthemn u'll cum to know da condition of electricity.

my ups remains only upto 5 min.

i don't hav any inverter nor generator.

plz let me solve these progs now.

if i ever ask again after my exams like then i requests da administrator to ban me.


PS: If any 1 having code plz provide me.


Anindya

hey incredible... pow stands for power function.. i.e. if we need to do 2 to the power 3 then we write pow(2,3) The POW function must have a prototype and it is included in the math.h header file.
Second thing if you don't have enough time to read ebooks and learn c++.. then how do you manage to hang around the digit forum for so much time... this is just an excuse for not studying c++.. if we are helping you that does not mean that you don't have to study c++.... if you are a computer freak and wanna study comp sc. or IT in the future then c or c++ is a must for everyone....

 

[ashu888ashu888]

mach wrote:

Hi ashu bro..
i havnt yet mentioned a site be4 i posted the tutz.. and i also dont see where mr incredible say he didnt find it useful

Mr.Incredible said this mach bro The-Incredible wrote:

BTW i've tried cprogramming.com provided by digit in three incredibly useful sites sectiond but didn't found anything helpful.

Look at the starting page of this thread buddy..neways i completely agree that we all r saying our point.. And i aslo agree with u buddy that even ur saying ur point..there is nothing to feel bad about it.. and im also not blaming any one..

Neways its all upto Mr.Incredible to learn or not to learn...

Cheers n e-peace...

 

[anubhav_har]

Hey ppl.. why has this post by Mr. Incredible been a post of such discussions... let Mr. Incredible do whatever he wants to... if he is giving us a question just answer it and leave him alone. If he does not want to learn or is not interested in C++ program leave him alone..