Question

this gives the amount 200003

#include <stdio.h>
int main(void){
int i = 0;
int x = 0, x15 = 0;
     for (i=0; i<1000; i++){
            if (i%3==0 || i%5==0){
                    x += i;
            }
            if (i%15==0){
                    x15 += i;
            }
    }
printf("%d'\n", x-x15);
return 0;
}

this gives the amount 233168

#include <stdio.h>
int main(void){
int i = 0;
int x3 = 0, x5 = 0, x15 = 0;

    for (i=0; i<1000; i++){

            if (i%3==0){
                    x3 += i;
            }
            if(i%5==0){
                    x5 += i;
            }
            if (i%15==0){
                    x15 += i;
            }
    }
printf("%d\n", x3+x5-x15);
return 0;
}

can anyone explain what’s different between the two? I would expect the two to provide the same output.

Answer 1

Multiple of 15 will be added to both x3 and x5 in the bottom code, so they are counted twice. In the top version, each is counted only once.