Thread: prime numbers using return 0

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ok thanks for the response. i guess i'm wrong about how i can do this. what i was getting at by trying to do it different was NOT using the % mod. i thought i could test for it being an integer by using something along the lines of - if return 0 (since int main() is used). basically i thought since it is expecting an integer then return 0 would mean an integer was returned and if a integer was returned using the division method then that means no remainder (since float is not being used). in other words i wouldn't need to use % mod. so basically if it goes through all its divisions in the loop up to the number inputed and and is still return 1 then it is prime. am i wrong about this use of returen 0 and return 1. can they not be used to test the condition without remainder. basicall if its return 0 on any pass then its not prime, right?
actually i was thinking while loop:
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#include <stdio.h>
int main()
{
int div=1,num;
printf("enter number");
scanf("%d",&num);
while div<num
{
div++
num/div
if return 0 then printf("not prime")
}
printf("prime")

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if the logic is right here i still need help with syntax. for exampled are my{} in right places, and can i use if then with return 0 that way. and the way its structured does that mean it will pass to printf("prime") if whats done in loop is never return 0?

Originally Posted by minty33

ok thanks for the response. i guess i'm wrong about how i can do this. what i was getting at by trying to do it different was NOT using the % mod. i thought i could test for it being an integer by using something along the lines of - if return 0 (since int main() is used). basically i thought since it is expecting an integer then return 0 would mean an integer was returned and if a integer was returned using the division method then that means no remainder (since float is not being used). in other words i wouldn't need to use % mod. so basically if it goes through all its divisions in the loop up to the number inputed and and is still return 1 then it is prime. am i wrong about this use of returen 0 and return 1. can they not be used to test the condition without remainder. basicall if its return 0 on any pass then its not prime, right?

I *was* thinking of return 0 or 1, being the return from another function within the program, instead of a return from main() itself.

What you've described is quite possible, but impractical. Your code as written now, gets input from the user (not *argv[]), so you would have to start your program, then enter the number to be checked, and then you'd get your answer AS THE PROGRAM ENDED.

So to check other numbers for prime, you'd have to restart your program for each number.

If you are repeatedly dividing, and acting upon the remainder of the division, aren't you using mod, in effect, by re-creating it?

Anyway, I'd keep your program running, and use the return from a test function you write, to determine whether a number is prime or not. It's easy enough to have the answer printed out, and let the program end after only one number, instead of using the return int from main().

num/div won't tell you if there was a remainder or not.

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