Here's a program to print prime numbers in C: 

#include 
#include 

int main() {
   int i, num, isPrime;
   printf("Enter an integer: ");
   scanf("%d", &num);
   for(i=2; i<=num; i++) {
      isPrime = 1;
      int j;
      for(j=2; j<=sqrt(i); j++) {
         if(i%j==0) {
            isPrime = 0;
            break;
         }
      }
      if(isPrime == 1) {
         printf("%d\n", i);
      }
   }
   return 0;
}

Explanation: 

The program takes an integer input from the user and stores it in the variable num.

A for loop is used to iterate from 2 to the input number num. 

Another for loop is used inside the first loop to check if the current number is divisible by any number between 2 and its square root. If it is divisible, the isPrime flag is set to 0, and the inner loop breaks. 

If the isPrime flag is still 1 after the inner loop, it means the number is prime, and it is printed to the console. 

Note: This program uses the sqrt function from the math.h library to calculate the square root of a number.