This C Program checks if a given number is prime. If a given number that has no other factor than that of the given number itself and 1, then that number is called as prime number.
Here is source code of the C program to check if a given number is prime. The C program is successfully compiled and run on a Linux system. The program output is also shown below.
* C program to check whether a given number is prime or not
* and output the given number with suitable message.
int num, j, flag;
printf("Enter a number \n");
if (num <= 1)
printf("%d is not a prime numbers \n", num);
flag = 0;
for (j = 2; j <= num / 2; j++)
if ((num % j) == 0)
flag = 1;
if (flag == 0)
printf("%d is a prime number \n", num);
printf("%d is not a prime number \n", num);
$ cc pgm16.c $ a.out Enter a number 23 23 is a prime number $ a.out Enter a number 15 15 is not a prime number
Sanfoundry Global Education & Learning Series – 1000 C Programs.