# Prime number program in C

Prime numbers are those numbers which are not divisible by any integer without 1 and itself. Composite number can be divisible by at least an integer without 1 and that number itself. 2 is the only even prime number as every even number can be divisible by 2.

Some example of prime numbers are 2, 3, 5, 7, 11, 13, 17, 19, 23……. . Prime numbers have many applications in not only mathematics but also in computer science. In this article we will discus more and give some example C program related to prime numbers in C programming.

## Checking prime numbers in C

``````#include<stdio.h>
int main(){
int num, i;

printf("Enter a number to check it prime or not : ");
scanf("%d", &num);

for (i = 2; i <= num/2; i++){
if (num % i == 0){
printf("\n%d is not a prime number.\n", num);
break;
}
}

if (i == num/2 + 1){
printf("\n%d is a prime number.\n", num);
}
return 0;
}``````

### Output of this prime number checking program ## Check prime number using function in C

``````// checking prime number in C
#include<stdio.h>

int checkPrime(int num){     // function to check prime
int i;

for (i = 2; i <= num - 1; i++)
{
if (num % i == 0)
return 0;
}
if (i == num)
return 1;
}

int main(){        // main program
int givenNum, result;

printf("Enter any number to check : ");
scanf("%d",&givenNum);

result = checkPrime(givenNum);      // calling function

if (result == 1){
printf("\n%d is a prime number.\n", givenNum);
}else{
printf("\n%d is not a prime number.\n", givenNum);
}
return 0;
}``````

### Output will be as follows ## Printing the list of prime numbers in C

``````// Printing list of prime numbers using C language
#include <stdio.h>
int main(){
int num, a = 3, count, b;

printf("How many prime number do you want to print?\n");
scanf("%d", &num);

if (num >= 1){
printf("The first %d prime numbers are : \n",num);
printf("2\n");
}

for (count = 2; count <= num;){
for (b = 2; b <= a - 1; b++){
if (a%b == 0){
break;
}
}
if (b == a){
printf("%d\n", a);
count++;
}
a++;
}
return 0;
}``````

### Output for this prime number printing program: You can print any integer using other methods too. So, try to write a program in your own.

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