CODEWITHSUNDEEP
c
user3443015
user3443015

Reputation:

Program is saying every number is prime number

I have created this C program that is supposed to tell me how many prime numbers are between 1-25, but it is printing that every number is prime number. Please Help

#include<stdio.h>

int main(void) {

int n = 1, counter = 0;
int i, flag = 0;

while ( n <= 25 ) 
{
    for ( i = 2; i <= (n/2); i++ ) 
    {
        if (n%i == 0) 
        {
            flag = 0;
        }
    }
    if (flag == 0) 
    {
        counter++;
        printf("%d is Prime Number.\n", n);
    } 
    else 
    {
        printf("%d is not Prime Number.\n", n);
    }
    n++;
}
return 0;
}

Upvotes: 0

Views: 126

Answers (2)

Sakthi Kumar
Sakthi Kumar

Reputation: 3045

flag = 0;

Your flag is always 0. You have to set it to 1, while entering the while loop

while ( n <= 25 ) {
    flag = 1; //<-- here
    for ( i = 2; i <= (n/2); i++ ) {

You can as well break in the segment, just for efficiency

if (n%i == 0) 
{
    flag = 0;
    break;
}

Upvotes: 6

LearningC
LearningC

Reputation: 3162

you can use the code as,

for ( i = 2; i <= sqrt(n); i++ ) 
    {
        if (n%i == 0) 
        {
            flag = 0;
        }
    }
    if (flag == 0) 
    {
        counter++;
        printf("%d is Prime Number.\n", n);
        flag=1;
    } 
    else 
    {
        printf("%d is not Prime Number.\n", n);
    }
    n++;

use sqrt() instead of n/2 program will be more efficient.

Upvotes: 0

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