ADMEC Multimedia > Web Development > Loops in C and C++

Loops are formed to “Repeat ” one or more continuous desired, number of times.

C offers following types of loops:
1. for loop
2. do while loop
3. while loop

for loop:

Syntax:

for(initialization of variables(s); condition; incrementation/decermentation of variable(s))
{
     statements(s);
}
  • when control enters for the first argument gets invoked for the first time only. Generally the initial value of the variable is given there. Ex: a=1;
  • if more than one variable are given here then it must be separated by comma(,).
  • After that control goes to second argument, where a condition is given.
  • if the condition is true control enters inside the loop and execute the statement given there.
  • After executing them control goes back for.
  • While going back, it automatically, internally invokes the third argument.
  • In the third argument generally the values of variable is incremented or decremented.
  • This way the loop works till the condition remain true.
  • As soon as the condition becomes false the control comes to the next line of the scope of for.

EX:1
Program:

#include<stdio.h>
#include<conio.h>
main()
{
   int a,b;
   clrscr();
   for(a=1; a<=5; a=a+1)
   {
        for(b=1; b<=5; b=b+1)
        {
             printf("*");
        }
        printf("\n");
    }
    getch();
}

Output:

*****
*****
*****
*****
*****

Remark:
The outer loop is the number of lines and the inner loop is controlling number of * in each line.

EX:2
For output:
*
**
***
****
*****

 In EX:1 program write:

for(b=1; b<=a; b=b+1)

EX:3
For output:
*****
****
***
**
*

#include<stdio.h>
#include<conio.h>
main()
{
   int a,b;
   clrscr();
   for(a=5; a>=1; a=a-1)
   {
       for(b=1; b<=a; b=b+1)
       {
           printf("*");
       }
       printf("\n");
    }
    getch();
}

EX:4
Output:

12345
1234
123
12
1

 In EX: 3 program write:

In the place printf(“*”);  write

printf(" %d", b);

While loop:

Syntax:

while (condition)
{
     statements(s);
}
  • One or more condition may be given with while.
  • If the condition is true, control enters inside the loop and executes the statement given there.
  • After executing them, control goes back to while and checks the condition again.
  • This way the loops works till the condition remains true.
  • As soon as the condition becomes false control comes to the next line of the scope of while.
  • The scope of while is define using
{
                
}

is optional , if a single statement is given with while otherwise it’s become compulsory.

  • While applying any type of loops only those lines should be given within the loop which needs to be repeated.

Program:

#include<stdio.h>
#include<conio.h>
main()
{
     int c=1;
     clrscr();
     while (c<=3)
     {
         printf("ADMEC \n");
         c=c+1;
     }
     getch();
}

Output:

ADMEC
ADMEC
ADMEC

Do-while

Syntax:

do
{
   statement(s);
}
while (condition);
  • The basic  difference between while and do while is that , do while works at least once.
  • While is a precheck loops, whereas do while is a post check loop.
  • When while is used no semicolon (;) is give after while , but in do while it is compulsory to give semicolon (;) after while.

Program:

#include<stdio.h>
#include<conio.h>
main()
{
     int a=1;
     clrscr();
     do
     {
         printf("%d \n", a);
         a = a + 1;
     }while (a<=3);
     getch();
}

output:
    1
    2  
    3

Loops are very important topic in any language and it is very typical to understand the concept of while, do-while and for. We try to understand some important point of loop statement in C and C++ in above topic. We also discuss control statement in C and C++ in our next blog….

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