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# C Program to Check Prime Number

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## What is Prime Number?

A positive integer that is divisible only by itself and 1.

Tips: It is recommended to use our online Prime Numbers calculator for better understanding.

## Examples

The following table provides few examples of prime numbers.

NumberDivisorResult
13 1, 13 Prime Number
15 1, 3, 5, 15 Not a Prime Number
47 1, 47 Prime Number

## Using for loop

In the following example, we will check whether the given number (7) is a Prime number or not using for loop.

### Example

C Compiler
#include <stdio.h> int main() { int num = 7; int i = 1; int count = 0; for(i=1; i<=num; i++) { if(num % i == 0) count++; } if(count == 2) printf("%d is a prime number", num); else printf("%d is not a prime number", num); return 0; }

## Using while loop

In the following example, we will check whether the given number (7) is a Prime number or not using while loop.

### Example

C Compiler
#include <stdio.h> int main() { int num = 7; int i = 1; int count = 0; while(num >= i) { if(num % i == 0) count++; i++; } if(count == 2) printf("%d is a prime number", num); else printf("%d is not a prime number", num); return 0; }

## Using do while loop

In the following example, we will check whether the given number (7) is a Prime number or not using do while loop.

### Example

C Compiler
#include <stdio.h> int main() { int num = 7; int i = 1; int count = 0; do{ if(num % i == 0) count++; i++; }while(i <= num); if(count == 2) printf("%d is a prime number", num); else printf("%d is not a prime number", num); return 0; }

## Prime Numbers between the Given Range

In the following example, we will find all the Prime numbers between 1 and 20.

### Example

C Compiler
#include <stdio.h> int main() { int start = 1; int end = 20; int count = 0; int i = 1; printf("Prime numbers between 1 and 20: \n"); for(start=start; start<=end; start++) { for(i=1; i<=start; i++) { if(start % i == 0) count++; } if(count == 2) printf("%d ", start); count = 0; } return 0; }

## Check Whether the Given Number is Prime or Composite

In the following example, we will check whether the given number is a Prime number or Composite number.

### Example

C Compiler
#include <stdio.h> int main() { int num, i, count = 0; printf("Enter a (int) number: "); scanf("%d", &num); for(i=1; i<=num; i++) { if(num % i == 0) count++; } if(count == 2) printf("%d is a prime number", num); else printf("%d is a composite number", num); return 0; }

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