Why this program is wrong ?

Question

1.00/5 (1 vote)

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when i made this program its showing 58 , when i compile its but its ans is 59 . Its not following bodmas is it?
program is below :=

plas help and a

What I have tried:

C++

#include <iostream>

using namespace std;

int main()
{

int x=3;
float y=5.6;
x=x+10*y;
cout<<x;
    return 0;
}

Posted 24-Dec-16 3:16am

Member 12920367

Updated 24-Dec-16 4:14am

CPallini

v3

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Comments

Philippe Mori 24-Dec-16 10:06am

Floating point values are not exact. So your have to properly round them when converting to avoid something like 58.9999 to be truncated to 58. As far as I known, the FPU will round numbers but C/C++ will truncate them.

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CPallini · Answer 1 · 2016-12-24T03:54:00

Solution 1

59 is the correct answer, isn't it?
The behaviour has nothing to do with bodmas violation, it follows from rounding rules of IEEE754[^], I believe.

Posted 24-Dec-16 3:54am

CPallini

OriginalGriff · Answer 2 · 2016-12-24T04:05:00

Probably, it depends on the compiler and system you are using: when I try it, I get 59.
The problem may be happening because you are mixing data types:

C++

x=x+10*y;
  ^  ^ ^
  |  | |
  |  | ---- float
  |  ------ integer
   -------- integer

When you multiply 10 * y there are two ways the system can do it: convert the integer 10 to a float and then multiply, or convert the float to a integer and then multiply - and that may produce different results if the conversion of "5.6" is rounded or truncated. Rounding would give you 6, truncation would give you 5, so you could conceivably get 50, 56, or 60 as an integer result. Which means you could get a final value of 53, 59, or 63 - but it's very unlikely that you would get 58.
Except...it could be a precision problem: Float Precision–From Zero to 100+ Digits | Random ASCII[^]
Try making everything floating point:

C++

float x = 3.0;
float y = 5.6;
x = x + 10.0 * y;
cout << x;

And I suspect your problem will just go away...

Patrice T · Answer 3 · 2016-12-24T04:14:00

Solution 3

floats do not store exact values, that is your problem.
Try:

C++

x=round(x+10*y);

With floats, 5.6 is something like 5.599999...
and x+10*y gives 58.99999... which is converted to 58 when stored in x.
round - C++ Reference[^]

Posted 24-Dec-16 4:14am

Patrice T

Updated 24-Dec-16 4:19am

v2

Comments

CPallini 24-Dec-16 11:14am

On my system 5.6 is 0x40b33333, which problably resembes 5.5999..
However 5.6*10 is 0x42600000 which is 56 (exponent 6, mantissa = 0.111B)
That is, according to IEEE754 rules, the result is rounded.

Afzaal Ahmad Zeeshan 24-Dec-16 14:10pm

5ed.