In this example, you will learn to print all prime numbers between two numbers (entered by the user).

To understand this example, you should have the knowledge of the following C programming topics:

To find all the prime numbers between the two integers,
`checkPrimeNumber()`

is created. This function
checks whether a number is prime or not.

```
#include <stdio.h>
int checkPrimeNumber(int n);
int main() {
int n1, n2, i, flag;
printf("Enter two positive integers: ");
scanf("%d %d", &n1, &n2);
printf("Prime numbers between %d and %d are: ", n1, n2);
for (i = n1 + 1; i < n2; ++i) {
// flag will be equal to 1 if i is prime
flag = checkPrimeNumber(i);
if (flag == 1)
printf("%d ", i);
}
return 0;
}
// user-defined function to check prime number
int checkPrimeNumber(int n) {
int j, flag = 1;
for (j = 2; j <= n / 2; ++j) {
if (n % j == 0) {
flag = 0;
break;
}
}
return flag;
}
```

**Output**

Enter two positive integers: 12 30 Prime numbers between 12 and 30 are: 13 17 19 23 29

If the user enters the larger number first, this program will not work as intended. To solve this issue, you need to swap the numbers first.