Suppose we want to make a program which will print your name 5 times. Then it will be very ineffective way to use the printf() function for 5 times. Instead of it we should look for something that will do that task for specific number of times automatically.
Well this is indeed possible. This is where loops comes in action. Loops are generally used to perform some task specific number of times. Similar to decision control instructions, in loops we also have to give some condition. And the program will execute task until the condition turns to be true.
There are three types of loops in C programming.
3. do while
while loop in C
This is the first loop and the second most commonly used loop in programs. It is generally used to execute a set of statements fixed number of times. Generally programmers use this loop when they already know how many times the task should be executed.
Syntax of while loop
increment loop counter
What is loop counter?
As I told you earlier that compiler doesn’t know how many times you want to perform some task. So to instruct the compiler we use loop counter. As its name suggests, it counts and instruct the while loop to stop executing the task.
|Flowchart of While Loop in C – Image Source|
Lets try to understand while loop with a simple program.
- In our program x is working as a loop counter. While declaring as a int variable I assigned a value 0 to it.
- After that I wrote the while loop with condition x<5. It means the loop will be executed till x is less than 5. To stop the loop x should contain the value 5.
- In the while loop I have given a printf() function to display the name.
- After that I have increased the loop counter by adding 1 to it.
- In the beginning compiler will check the condition to enter the while loop. But as I have assign the value 0 to it. So the condition will turn true.
- After that the control will shift inside the loop and it will display the message.
- Now the loop counter which is x increased by 1. Then the new value of x will be 1.
- Now the compiler again check the condition of while loop. Now x contains the value 1 which is still true. Now it will again print the message and the value of x will again increase.
- The process will be carried out until x becomes 5. When x will become 5 then compiler again check the condition but this time it will return false and the while loop will end.