# C program to display prime numbers between two numbers using function and without using function

In this example, you will learn about C program to display prime numbers between two numbers interval or in a given range by the user with and without using the function.

### What is prime number ?

A prime number is a natural number that is divisible by 1 and itself only.

For example: 2, 3, 5, 7 …

Please go through following articles of C programming to understand the concept of the program.

## C program to display prime numbers between two integers without using function

``````#include <stdio.h>

int main ()
{
int num1, num2, i, j, flag;

printf("Enter two numbers: ");
scanf("%d %d", &num1, &num2);

printf("Prime numbers between %d and %d are:\n", num1, num2);
// Displaying prime number between num1 and num2
for (i = num1 + 1; i < num2; ++i)
{
flag = 0; //flag is set to 0
for (j = 2; j <= i/2; ++j)
{
if (i % j == 0)
{
flag = 1;
break;
}
}
if (flag == 0) //if flag == 0, then display i
printf("%d\t", i);
}
return 0;
}
``````

Output ## C program to display prime numbers between two integers using function

``````#include <stdio.h>

int displayPrimeNumber (int x); //function prototype
int main ()
{
int num1, num2, i, flag;

printf("Enter two numbers: ");
scanf("%d %d", &num1, &num2);

printf("Prime numbers between %d and %d are:\n", num1, num2);
// Displaying prime number between num1 and num2
for (i = num1 + 1; i < num2; ++i)
{
if (flag == 0) //if flag == 0, then display i
printf("%d\t", i);
}
return 0;
}

{
int j, flag = 0;
for (j = 2; j <= x/2; ++j)
{
if (x % j == 0)
{
flag = 1;
break;
}
}
return flag;
}
``````

Output Explanation
The first example displays all prime numbers without using user defined function.

However, we have used `displayPrimeNumber` user defined function for same purpose.

The sole purpose of `displayPrimeNumber` user defined function is to check the number is prime or not and set the value of `flag`.