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:

```
#include <stdio.h>
int main() {
int low, high, i, flag;
printf("Enter two numbers(intervals): ");
scanf("%d %d", &low, &high);
printf("Prime numbers between %d and %d are: ", low, high);
while (low < high) {
flag = 0;
// if low is a non-prime number, flag will be 1
for (i = 2; i <= low / 2; ++i) {
if (low % i == 0) {
flag = 1;
break;
}
}
if (flag == 0)
printf("%d ", low);
++low;
}
return 0;
}
```

**Output **

Enter two numbers(intervals): 20 50 Prime numbers between 20 and 50 are: 23 29 31 37 41 43 47

In this program, the `while`

loop is iterated (
`high-low-1`

) times.

In each iteration, whether `low`

is a prime number or not is
checked, and the value of `low`

is incremented by
`1`

until `low`

is equal to `high`

.

Visit this page to learn more about how to check whether a number is prime or not.

If the user enters the larger number first, the above program doesn't work as intended. You can solve this issue by swapping the numbers.

```
#include <stdio.h>
int main() {
int low, high, i, flag, temp;
printf("Enter two numbers(intervals): ");
scanf("%d %d", &low, &high);
// swap numbers if low is greather than high
if (low > high) {
temp = low;
low = high;
high = temp;
}
printf("Prime numbers between %d and %d are: ", low, high);
while (low < high) {
flag = 0;
for (i = 2; i <= low / 2; ++i) {
if (low % i == 0) {
flag = 1;
break;
}
}
if (flag == 0)
printf("%d ", low);
++low;
}
return 0;
}
```

Visit this page to learn how you can display all the prime numbers between the two intervals by creating a user-defined function.

```
```