Syntax of while loop:

while(condition) {

statement; // body of the loop

}

Code flow for while loop:

First, condition is evaluated, if condition is true then statement is evaluated. Loop will exit only when condition is false. It does not have all the 4 parts discussed in this article.

While you could make it contain all 4 parts by doing as below.

initialize_counter;

while(condition) {

statement; // body of the loop

change_condition;

}

**Program that checks number for prime**

Prime number is a number which is evenly divisible by 1 or itself only(More details)

*Strategy:*If the number is n, and it is divisible by any number(x) between 2 and n/2 then it is not prime otherwise it is prime.

#include <stdio.h> int main() { int n = 7913; int x = 2; while(((n % x) != 0) && (x < n/2)) { x++; } if((n % x) == 0) { printf("%d Not prime, because it is divisible by %d \n", n, x); }else { printf("%d is prime\n", n); } }

Output of above program is as follows

```
7913 Not prime, because it is divisible by 41
```

*Explanation*

Condition in while loop (((n % x) != 0) && (x < n/2)) is making sure n is not divisible by x and x is always smaller than n/2. Body of loop only contains increment, which makes sure x has all the value between 2 to n/2. Loop will exit if n is divisible x or x become greater than n/2. In the end if statement distinguishes above two condition, to determine whether it is prime or not.

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