environment: codeblock
compilation environment: mingw32-gcc.exe-pedantic-Wextra-Wall-std=c99-c path
Code:

-sharpinclude <stdio.h>

int main(){
    FILE *fin, *fout;
    fin = fopen("data.in","rb");
    fout = fopen("data.out","wb");
    int m, n;
    int line = 1;
    while(fscanf(fin, "%lld%lld", &n, &m) == 2){
        if(m == 0 && n == 0) break;
        double sum = 0;
        for(int i=n;i<=m;iPP){
            //double j = i; //
            sum += 1 / ((double)i * (double)i);
        }
        fprintf(fout, "Case %d: %.5f\n", line, sum);
        linePP;
    }
    fclose(fin);
    fclose(fout);
    return 0;
}

question:
when the question line is double j = I uncommented, data.out will have output, but when the question line is commented, data.out will not have output, why?
isn"t this business pointless?

input data is:

2 4
65536 655360
0 0