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copied!<p>First, make sure your code has appropriate whitespace. This will help you realize when things aren't lined up like you think they are.</p> <pre><code>#include <stdio.h> int main() { int num, i; printf("Number [1-100]:? \n"); scanf("%d", &num); while(num>0 && num <101){ if (num==1||num==2) printf("Prime\n"); for(i=2; i<=num/2; ++i) { if (num%i==0) { printf("Non-prime,divisible by %d\n",i); break; } else { printf("Prime\n"); break; } } printf("Number[1-100]:? \n"); scanf("%d",&num); } printf("Done\n"); } </code></pre> <p>Now you should realize that your else statement happens on the first check! So when 3 is not divisible by 2, it prints "prime."</p> <p>And then it breaks out of the loop.</p> <p>And this happens for EVERY number. All your program is doing is checking to see if numbers are divisible by 2.</p> <p>If you wrote "Odd" instead of "Prime" it would at least be correct there.</p> <p>This is the kind of problem where setting a flag might be useful (there are other ways to do this, but this is one way). So you could set a flag, say <code>int isPrime = 1;</code></p> <p>Now, if you find out that the number is not prime, you simply set <code>isPrime = 0;</code>.</p> <p>Finally, at the end of the for loop (let me repeat: AFTER the for loop finishes), you need to check that variable. And you can say,</p> <pre><code>if (isPrime == 1) { printf("Prime\n"); } else { printf("Non-prime."); } </code></pre> <p>I'll let you figure out how to print the divisor :)</p> <p>(For reference, correctly using the flag would look like this -- and for clarity I removed the 'feature' in which it continuously looped)</p> <pre><code>#include <stdio.h> int main() { int num, i; int isPrime = 1; printf("Number [1-100]:? \n"); scanf("%d", &num); for(i=2; i<=num/2; ++i) { if (num%i==0) { isPrime = 0; break; } } if (isPrime == 1) { printf("Prime\n"); } else { printf("Non-prime."); } printf("Done\n"); } </code></pre>

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