program that tells if a number is prime - c

Question

you enter a number and the program will find if the number is prime or not
so when I enter the number 7 for the first time it will show you 'the number is prime'
then I enter 8 and it will show you 'the number is not prime'
after that I re_enter the number 7 and it will show you 'the number is not prime'
I don't know where is the problem
please help me
an example photo from here
and my code is :
#include <stdio.h>
#include <stdlib.h>
int main (void){
int n;
int t;
int isPrime=0;
char var;
while(var!='q'){
printf("q=quit p=prime :");
fflush(stdin);
scanf("%c",&var);
if(var=='p'){
printf("plz put the number value :");
scanf(" %d",&n);
for(t=2;t<=n/2;t++){
if (n%t==0){
isPrime=1;
break;
}
}
if(isPrime==0){
printf("%d is a prime number\n",n);
}
else{
printf("%d is not a prime number\n",n);
}
}
else if(var=='q'){
printf("thank you bye\n");
break;
}
else{
printf("a wrong letter\n");
}
}
return 0;
}

Answer 1

You need to set isPrime to 0 each time the user enters a number. Otherwise, it still holds the value from the previous number.
Move the variable declaration
int isPrime = 0;
inside the while loop.
BTW, isn't that variable name backwards? You set it to 1 (i.e. true) when you discover that there's a number that divides it equally. But that's when the number is not prime.

Answer 2

You forgot to reset isPrime back to zero inside the "while" loop.
By they way, looks like you are doing this as a learning exercise. That's good, there's no better way to learn than to try things out.
Here's a tip in C, any non-zero value is treated as "true", and zero is treated as "false". So instead of this:
if (myFlag==1) { ... do something }
Just write this:
if (myFlag) { ... do something }