C program to print prime numbers between two numbers

Prime numbers are the numbers which have only two factors, 1 and the number itself. That means, they are not divisible by any number other than one and the number itself.

In this article, we’ll learn how to check whether a number is prime or not, with and without using function. But before that, we’ll write a program to print prime numbers from 1 to 200.

This C program prints prime numbers from 1 to 200. This algorithm can also be used to check whether a number is prime or not.

Program: C program to print prime numbers from 1 to 200

#include<stdio.h>
int main()
{
    int n,i,flag;
    for(n=1; n<=200; n++)   /*iterate over numbers from 1 to 200*/
    {
        flag=0;
        for(i=2;i<=(n/2);i++)
        {
           if((n%i)==0)         /* check prime or not*/
           {
            flag=1;
            break;
           }

        }
        if(flag==0)
            printf("%d ",n);
    }
    printf("\n");
    return 0;
}

Output: Prime numbers from 1 to 200

1 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97 101 103 107 109 113 127 131 137 139 149 151 157 163 167 173 179 181 191 193 197 199

Now, we’ll write a program to check whether a number is prime or not using function. The same algorithm is used to serve this purpose.

Program: C program to check whether a number is prime or not using function

#include<stdio.h>
int checkPrime(int);
int main()
{
    int n,i,flag;
    printf("Enter a number: ");
    scanf("%d", &n);
    flag = checkPrime(n);
    if(flag == 1)
        printf("%d is not a prime number.", n);
    else
        printf("%d is a prime number.", n);
    printf("\n");
    return 0;
}
int checkPrime(int a){
    int i;
    for(i=2;i<=(a/2);i++)
    {
        if((a%i)==0)         /* check prime or not*/
            return 1;
    }
        return 0;
}

Output:

Sample output #1:

Enter a number: 4337
4337 is a prime number.

Sample output #2:

Enter a number: 4239
4239 is not a prime number.

Challenge: Write C program to check whether a number is prime or not in the comments.

In this article, we learnt to write program in C to check prime numbers and to print prime numbers between two numbers.

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