C Program to generate prime numbers between two numbers | prime numbers between n1 and n2

by Venkat · December 18, 2014

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This article is one of the article in Series of Prime number generation programs. In my previous articles i discussed about
What is prime Number and C program to Check given number is Prime or Not,
Check given Number is Prime or not Using Square Root(sqrt) Function.(Efficient way).
Now we will discuss about c program to generate prime numbers between two numbers.

Description :

This program accept two integers from user and and generates all prime numbers between those two Numbers. here i am using two loops one is Outer loop and second one is Inner loop. outer loop will starts with n1( first number of user) and ends with n2 (user’s second number ). Inner loop is normal prime number logic loop starts with 2 and ends with n/2 (you can use sqrt(n) ).

Program :

#include<stdio.h>
void main()
{
        int i,j,cnt,n1,n2;
        printf(“Enter two Numbers : “);
        scanf(“%d%d”,&n1,&n2);
        // n2 must be grater than n1, so check it first
        if(n1 > n2)
        {
                printf(“n2 must be greater than n1 n“);
                return;
        }
        printf(“prime Numbers between %d and %d are : “,n1,n2);
        for(i=n1; i<=n2; i++)
        {
                // use one count variable, make it as 0 for every iteration
                cnt = 0;
                // loop for checking number is prime or not
                for(j=2; j<=i/2; j++)
                {
                        if(i%j == 0)
                        {
                                cnt++;
                                break;
                        }
                }
                if(cnt == 0)
                printf(“%d “,i);
        }
        printf(“n“);
        return ;
}