Remember to create a list of the steps using comments you want your program to perform so that you can keep track of your completeness as you go.

loops.c

//
//  main.c
//  Loops
//
//  Created by Curt on 2/5/13.
//  Copyright (c) 2013 Curt. All rights reserved.
//

#include <stdio.h>

int main(int argc, const char * argv[])
{
    //count backwards by 3 from 99 to 1
    for (int x = 99; x > 0; x -= 3) // <-- see how I declared x's type as an int inside the loop?  there's a reason.
    {
        //see what numbers are divisible evenly by 5
        if (x % 5 == 0)
        {
            //tell me when you find one
            printf("Found one! - %d.\n", x);
        } 
        
    }
    
    return 0;
}