###### C++ Functions

C++ Program to Display Prime Numbers Between Intervals Using Function

# C++ Program to Display Prime Numbers Between Intervals Using Function

In this example, we will learn a program to print all prime numbers between two numbers (entered by the user) by making a user-defined function.

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

## Example: Program to Display Prime Numbers Between two Intervals

``````# include <iostream>
using namespace std;

int main() {
int n1, n2;
bool flag;

cout << "Enter two positive integers: ";
cin >> n1 >> n2;

// swapping n1 and n2 if n1 is greater than n2
if (n1 > n2) {
n2 = n1 + n2;
n1 = n2 - n1;
n2 = n2 - n1;
}

cout << "Prime numbers between " << n1 << " and " << n2 << " are: ";

for(int i = n1+1; i < n2; ++i) {
// If i is a prime number, flag will be equal to 1

if(flag)
cout << i << " ";
}

return 0;
}

// user-defined function to check prime number
bool isPrime = true;

// 0 and 1 are not prime numbers
if (n == 0 || n == 1) {
isPrime = false;
}
else {
for(int j = 2; j <= n/2; ++j) {
if (n%j == 0) {
isPrime = false;
break;
}
}
}

return isPrime;
}``````

Output 1

```Enter two positive integers: 12
55
Prime numbers between 12 and 55 are: 13 17 19 23 29 31 37 41 43 47 53 ```
##### Working

To print all prime numbers between two integers, `checkPrimeNumber()` function is created. This function checks whether a number is prime or not.

All integers between n1 and n2 are passed to this function.

If a number passed to `checkPrimeNumber()` is a prime number, this function returns true, if not the function returns false.

If the user enters the larger number first, this program will swap the numbers. Without swapping, this program won't work.

## Next Example

We hope that this Example helped you develop better understanding of the concept of "Display Prime Numbers Between Intervals Using Function" in C++.

Keep Learning : )

In the next Example, we will learn about C++ `Prime Number By Creating a Function`.