Question

    printf("%.2lf\n",odd);                        //(1)
    printf("%.2lf\n",37.975);                     //(2)
    printf("%.2lf\n",(odd*0.65 -1)*2);            //(3)
    printf("%.3lf\n",(odd*0.65 -1)*2);            //(4)

Below is the output:

30.75

37.98

37.97

37.975

Why the output of expression(3) is not 37.98 ?

I use g++.

Answer 1

This is likely due to floating point rounding errors. The result of (odd * 0.65 - 1) * 2 is likely 37.97499999999999 or something close to (but less than) 37.975. By the usual rounding rules, this is rounded down to 37.97 in the output.