Loops in c

Repetition of a set of instructions in a program is called loops in c.

Loops in c involve repeating some portion of the program either a specified number of times or until a particular condition is being satisfied.

Looping increases the versatility of the program.

There are three loops in c that can be used to repeat some portion of a program.

1.           while loop

2.           for loop

3.           do-while loop

Let us discuss each loop one by one

  while loop  

There is some portion in a program that we want to repeat a fixed number of times in such cases we can use a while loop.
 

Let us take an example,

 Query-  print the table of 7

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
#include<stdio.h>
#include<conio.h>
void main()
{
  int num=7;
  int count=1,table;

  while(count<=10)
   {
    table=num*count;
    printf(“%d*%d=d”,num,count,table);
    count++;  
   }
   getch();
 }

while-loop-c

while-loop-c

Flow chart:

while-loop-c

  • The program is, printing the table of 7.
  • Now to print the table of seven, we need logic or algorithm that will process 10 times.
  • For this, here we need a loop, and a condition where a loop will process 10 times, i.e., 10 times the logic should process.
  • The second thing we need a counter that should be set to 1 and gets incremented until the condition applied is valid.
  • We have used while loop and under ( ) braces of while loop we have applied the condition, “counter <=10”.
  • Then we have applied the logic for the table.
  • After the first process, we have incremented the counter and, the counter gets incremented and, logic gets processed till the counter is 10.
  • When the counter becomes 11, the condition gets false and, the loop gets over.

Important points to remember

 

1. Instead of count++ we can also write count=count+1 or count+=1.                       

You must be knowing that (++) is increment operator and (--) is decrement operation.

Increment operator (++) = increment operator is used to increment the loop counter. 

The decrement operator (--) = decrement operator is used to decrementing the loop counter. 


2. By using (++) or (--) operator, we can only increment or decrement by 1.              

Using count=count+1 format, we can increment or decrement by other than 1.   

eg. count=count+2, count=count +3   these is increment.                                          

count = count-2, count= count -3  these is decrement.                                                

Note that here count is just an integer variable that we have used as a loop counter. We can use any other variable name as per our choice.



3. It is not necessary that the loop counter should be int we can also use a float loop counter.

#include<stdio.h>
int main()
{
  float i=0.1;
  while(i<=0.10)
{
  printf(“hello world”);
  i=i+0.1;
}
return 0;
}

We can also decrement the floating loop.       

4.  While(i<=10);

#include<stdio.h>
 int main()
 {
  int i=1;
  while(i<=10);
  {
   printf(“hello world”);
   i++;
  }
 return 0;
 }

·    As you can see in the above program, after the while statement there is a semicolon (;).

·     while(i<=10);   here is a semicolon after the while statement, the semicolon is a sign of termination, which means when we give termination symbol (;) after the while statement, the while loop gets terminated till  (;). i.e., the statements present in the curly braces{} which are the body of a while loop will not be considered as the body of a while loop. The statements under curly braces will not be part of the while loop.

Hence, the program will run infinitely as the value of subscript "i" is always 1. The subscript "i" will not be incremented and the while loop will run infinitely.  There will be no error in the program.
 
4. Post-increment 
#include<stdio.h.
 int main()
 {
  int i=0;
  while(i++<=10)
  {
   printf(“%d\n”,i);
  }
 return 0;
 }

·        In the program above, the condition and loop counter incrementation is done under a single while( ) round braces. We have not used a separate line for the loop counter.

·    In the line while(i++<=10) value of subscript "i" is first compared with the condition after that it is incremented.

·    i++ is called as post increment.

·   After checking the condition, the value "i" increments and, perform the operation under while loop body under the { } curly braces.

·     That is why subscript "i" should be initialized to 0, not 1.

5. Pre-increment
#include<stdio.h>
 int main()
 {
  int i=0;
 while(++i<=10)
   {
    printf("%d\n",i);
   }
  return 0;
 }

·    The only difference between the previous program and this program is ++i.

·    Here first the value of subscript "i" is incremented then it is compared with the condition. Hence incrementation of "i" becomes before the comparison.

·    ++i is called as pre-increment.

    To know more about increment and decrement operator follow the below link,

       increment and decrement operator in c

  

      See Also:

   for loop
   do-while loop
   break statement
   continue statement