Calculation returns zero instead of expected result

Question

I am trying to do a simple calculation : ( (45/100) - (20+50)/200 )*(10+5)

I am expecting the answer to be 1.5 but when the programme is compiled , it shows 0.

Can someone figure this out for me

#include <iostream>
using namespace std;

int main()
{
   float   CivIndex = ( (45/100) -  (20+50)/200 )
                  *(10+5);

   cout<<CivIndex; // expect 1.5 but getting 0
}

You are doing [integer division](http://mathworld.wolfram.com/IntegerDivision.html). You need to specify float constants, e.g. `45.0f / 100.0f`. — i_am_jorf, Oct 07 '13 at 16:40

score 5 · Accepted Answer · answered Oct 07 '13 at 16:40

5

Integer division!

(45 / 100) equals 0 when evaluated as an integer, not 0.45 as you'd been hoping.

Make either numerator or denominator a float to get the expected result:

(45.0 / 100)

answered Oct 07 '13 at 16:40

James Cronen

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score 3 · Answer 2 · answered Oct 07 '13 at 16:42

What you are doing is integer division, and integer division rounds the result to the closest integer. To correct your code, change it to:

#include <iostream>
using namespace std;

int main()
{
   float   CivIndex = ( (45.0/100.0) -  (20.0+50.0)/200.0 )
                  *(10.0+5.0);

   cout<<CivIndex; // expect 1.5 but getting 0
}

Note: not all .0 are needed, but just put them to be sure.

score 2 · Answer 3 · answered Oct 07 '13 at 16:40

2

You are doing integer division.

Specify it as float constants

 float   CivIndex = ( (45./100) -  (20+50)/200. )*(10+5);
                        ^ Notice decimal points^

answered Oct 07 '13 at 16:40

P0W

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score 2 · Answer 4 · answered Oct 07 '13 at 16:40

All your constants are ints, therefore, the compiler is doing integer math. 45/100 as an int is 0. So is 70/200. 0 - 0*15 = 0. You need to tell the compiler that your constants are floats: 20f, or 20.0 would both work. (For each operation, if at least one constant is a float, the operation will be treated as floating point math.)

score 2 · Answer 5 · answered Oct 07 '13 at 16:40

In C and several other languages diving two integers result in an integer (integral division). That is 45 / 100 in your code will result in 0 instead of the expected 0.45

The fix is simple: convert one of the operands to floating point.

float   CivIndex = ( (45/100.0) -  (20+50)/200.0 )
              *(10+5);

score 1 · Answer 6 · answered Oct 07 '13 at 16:40

1

You are hoping the integer division as 0.45 but that is actually 0

Try to change this as:

 float   CivIndex = ( (45.0/100) -  (20.0+50.0)/200 )
              *(10+5);

answered Oct 07 '13 at 16:40

Rahul Tripathi

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score 0 · Answer 7 · edited Oct 07 '13 at 17:29

0

You are essentially evaluating an expression containing only integers. So the result will be an integer. You can use casts on the final result of the integer expression. e.g..

int a=20;float b; b=(float)a;cout<<"b: "<<b;

Please confirm the syntax.

Or as stated above, you can also make one of you operands as a float/double(if your requirement permits).

edited Oct 07 '13 at 17:29

Dave Hogan

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answered Oct 07 '13 at 17:11

user2852095

1

Calculation returns zero instead of expected result

7 Answers7