if statement in code is not working

[momon]

Hi everyone.

This is a very easy question ( or so it seems ).

Here is a short piece of code:

#include <stdio.h>

int main() {

int Phase = 3;
double kva = 1000;

if( kva > (1000 * (Phase / 3.0)) )
printf(&quot;greater than&quot;
else
printf(&quot;less than&quot;

return 1;
}

I am compiling this program under Borland C++ 5.02.

The funny thing is that a trace of the program reveals the expression ( kva > (1000 * (Phase / 3.0)) ) to be false. Yet the resulting output is &quot;greater than&quot;.

Can anyone explain why?

Thanks

 

[JasonDeckard]

Your code executes as expected for me (I get &quot;less than&quot with hpux-cc.

 

[momon]

haha... i love when this kind of thing happens. thanks for running the code.

 

[victorv]

hi,
why do you not declare a var as

double x ;

x=1000 * (Phase / 3.0) ;

PRINT x
and see if is <=> to 1000

Compilator is not a man that knows fractions; I'ld prefere write :

x = ( (double)Phase * 1000.0 ) / 3.0

(probably you'll obtain more floating precision)

bye

 

[momon]

hi.
thanks for reading the post victorv.

The compiler does know about fractions and type conversions in expressions.

For example,
int / int results in an int. e.g. 1/3 = 0
double / int results in a double e.g. 1.0/3 = 0.333...
int / double also results in double e.g. 1/3.0 = 0.333...

but to be safe we can always cast Phase to a double as you did.

anyone else have any ideas what is causing this problem?

 

[victorv]

hi,

if you use an intermediate var x

x = ( (double)Phase * 1000.0 ) / 3.0

PRINT or debug it here, an then make the test

if( kva >= x )
printf(&quot;greater or equal than&quot;
else
printf(&quot;less than&quot;


which is the result ?


bye

 

[momon]

The result is &quot;greater than or equal&quot;. However, it is in fact equal since replacing the condition ( kva >= x ) with ( kva > x ) results in &quot;less than&quot; being printed.

So the use of an intermediate variable does solve the problem. Thanks.

So to sum up.

The following code:

int main() {

int Phase = 3;
double kva = 1000, x;

x = 1000 * Phase/3.0;

if( kva > x )
printf(&quot;greater than&quot;
else
printf(&quot;less than or equal&quot;

return 1;
}

returns the correct result of &quot;less than or equal&quot;.

However, the following logically identical code

int main() {

int Phase = 3;
double kva = 1000;

if( kva > (1000 * Phase/3.0) )
printf(&quot;greater than&quot;
else
printf(&quot;less than or equal&quot;

return 1;
}

returns &quot;greater than&quot;.

In conclusion: There is something seriously wrong.