## Example #1: Display Prime Numbers Between two Intervals

```
#include <stdio.h>
int main()
{
int n1, n2, i, flag;
printf("Enter two numbers(intevals): ");
scanf("%d %d", &n1, &n2);
printf("Prime numbers between %d and %d are: ", n1, n2);
while (n1 < n2)
{
flag=0;
for(i=2; i<=n1/2; ++i)
{
if(n1%i == 0)
{
flag=1;
break;
}
}
if (flag == 0)
printf("%d ",n1);
++n1;
}
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 `(n2 - n1 - 1)`

times.

In each iteration, whether `n1` is a prime number or not is checked and the value of `n1` is incremented by 1 until `n1` is equal to `n2`.

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.

## Example #2: Display Prime Numbers Between two Intervals When Larger Number is Entered first

```
#include <stdio.h>
int main()
{
int n1, n2, i, flag, temp;
printf("Enter two numbers(intevals): ");
scanf("%d %d", &n1, &n2);
//swapping numbers if n1 is greater than n2
if (n1 > n2) {
temp = n1;
n1 = n2;
n2 = temp;
}
printf("Prime numbers between %d and %d are: ", n1, n2);
while (n1 < n2)
{
flag=0;
for(i=2; i<=n1/2; ++i)
{
if(n1%i == 0)
{
flag=1;
break;
}
}
if (flag == 0)
printf("%d ",n1);
++n1;
}
return 0;
}
```

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