Code which prints YES if the given number is prime and NO if it is not in C

Question

I have tried the following code

#include<stdio.h> int main(void) { int t,i, N, j,count=0; printf("t\n"); scanf("%d",&t); for(i=0;i<t;i++) { printf("N\n"); scanf("%d",&N); for(j=1;j<=N;j++) { if(N%j==0) { count++; } } if(count==2) { printf("YES\n"); } else { printf("NO\n"); } } return 0; }

But it just prints the first test case correctly, for eg. I gave the first test case as 3 it Prints yes, and 7 as the second test case it prints NO. What's the issue I am not able to figure out with this code. Similarly, if I enter the first test case as 7 it prints YES, and enters 3 as the second case it prints NO.

Did you reset the variable count to zero after every input? — iBug
– iBug, Commented Jun 24, 2021 at 6:06

MikeCAT · Accepted Answer · 2021-06-24 06:06:04Z

1

You forgot to initialize count for each query. Add initialization to fix.

 printf("N\n"); scanf("%d",&N); count=0; /* add initialization here */ for(j=1;j<=N;j++) {

answered Jun 24, 2021 at 6:06

MikeCAT

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3 Comments

Aviral Mishra Over a year ago

Yes, Thanks, it's working, but can you plz explain the purpose of initializing it, at that place particularly. I mean I initialized count=0 in beginning, why its not counted??

MikeCAT Over a year ago

Initialization is for having it doing the computation from the beginning. Your initialization is done only once before reading the number of query and it won't be helpful to prevent queries from being influenced by previous query.

Gerhardh Over a year ago

@AviralMishra You should start using a debugger as soon as possible. Step through your code and watch values of your variables. This should answer that question about "why" immediately.

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