4 – Best C program to check prime number

C program to check prime number

Prime number is a number which is only divisible by itself or by one. Following  C program will help to understand the logic to check whether the number is prime or not.

Logic to check prime number in C programming

#include <stdio.h>
int main()
{
int num,i,flag=0;
printf("Enter any number : ");
scanf("%d", &num);

if(num==1)
{
printf("1 is not a prime or composite number");
}
else
{
for (i=2; i<=num/2; i++)
{
if (num%i == 0)
{
flag = 1;
break;
}
}
if(flag==0)
{
printf("%d is a prime number", num);
}
else
{
printf("%d is not a prime number", num);
}
}
return 0;
}

 

Output :

Enter any number : 23

23 is a prime number

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