What happens if we use extra parenthesis() in mathematical expression?

Question

double res = (double)((a*b)/(a+b));

After trying the above code with inputs 80,70 I am getting the output 37 not 37.333 but after removing one parenthesis i got the right answer.

The right code is:

double res = (double)(a*b)/(a+b);

I am using: gcc version 9.3.0 (Ubuntu 9.3.0-10ubuntu2)

1. First Case double res = (double)((a*b)/(a+b)); In this case, for the input 80 and 70, the evaluation goes as -> res = (double)((70*80)/(70+80)) = (double)((5600)/(150)) = (double)(37) = 37 2. Second Case double res = (double)(a*b)/(a+b); In this case, for the input 80 and 70, the evaluation goes as -> res = (double)(70*80)/(70+80) = (double)(5600)/(150) = 5600.0/150 = 37.33 — Abhishek Bhagate, Sep 07 '20 at 18:14
Worked for me. I even simplified with less parens and no unnecessary cast. `double a = 80; double b = 70; double res = (a*b)/(a+b);` — Eljay, Sep 07 '20 at 21:39

Tony Tannous · Accepted Answer · 2020-09-07T18:14:21.433

2

double res = (double)((a*b)/(a+b));

Casting to double after integer math is applied, where values might have been truncated. Resort to operator precedence.

double res = (double)(a*b)/(a+b);

Here the cast is performed before the divison.

edited Sep 07 '20 at 18:14

answered Sep 07 '20 at 18:08

Tony Tannous

"rounded down' - they are truncated. I know, distinction without a difference :) – Vlad Feinstein Sep 07 '20 at 18:10
@VladFeinstein agreed. – Tony Tannous Sep 07 '20 at 18:14
@VladFeinstein — they’re not the same. Truncating `-1.5` gives `-1`. Rounding it down gives `-2`. – Pete Becker Sep 07 '20 at 22:25
@PeteBecker it depends on your definition of "down" :) I think of it is "towards 0" – Vlad Feinstein Sep 08 '20 at 16:10

1 Answers1