>>110
- int B[3][3];
+ double B[3][3];

- fscanf(fpin, "%d", &B[i][j]);
+ fscanf(fpin, "%lf", &B[i][j]);

- fprintf(fpout, "%3d", B[i][j] / 3);
+ fprintf(fpout, "%g", B[i][j]/3);

とりあえずこんなところでどうよ。