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

```
#include <iostream>
using namespace std;
int main() {
int low, high, i;
bool isPrime = true;
cout << "Enter two numbers (intervals): ";
cin >> low >> high;
cout << "\nPrime numbers between " << low << " and " << high << " are: " << endl;
while (low < high) {
isPrime = true;
if (low == 0 || low == 1) {
isPrime = false;
}
else {
for (i = 2; i <= low / 2; ++i) {
if (low % i == 0) {
isPrime = false;
break;
}
}
}
if (isPrime)
cout << low << " ";
++low;
}
return 0;
}
```

**Output**

Enter two numbers (intervals): 0 20 Prime numbers between 0 and 20 are: 2 3 5 7 11 13 17 19

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.

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

```
#include <iostream>
using namespace std;
int main()
{
int low, high, temp, i;
bool isPrime;
cout << "Enter two numbers (intevals): ";
cin >> low >> high;
//swapping numbers if low is greater than high
if (low > high) {
temp = low;
low = high;
high = temp;
}
cout << "\nPrime numbers between " << low << " and " << high << " are:" << endl;
while (low < high) {
isPrime = true;
if (low == 0 || low == 1) {
isPrime = false;
}
else {
for (i = 2; i <= low / 2; ++i) {
if (low % i == 0) {
isPrime = false;
break;
}
}
}
if (isPrime)
cout << low << " ";
++low;
}
return 0;
}
```

**Output**

Enter two numbers (intervals): 20 0 Prime numbers between 0 and 20 are: 2 3 5 7 11 13 17 19

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