Example to print all prime numbers between two numbers (entered by the user). This problem is solved using nested for loop and if...else statement.

To understand this example, you should have the knowledge of 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;
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 on how to check whether a number is prime or not.

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

```
#include <stdio.h>
int main()
{
int low, high, i, flag, temp;
printf("Enter two numbers(intevals): ");
scanf("%d %d", &low, &high);
//swapping numbers if low is greater 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 prime numbers between two intervals by using a user-defined function.