question about subtracting 2 values in C

[BALIstik916]

if i were to find the difference between 2 values of time (in military form) such as 1200 and 1400 and im using the variable type long and then using the absolute value function

long timediff = labs(timeout - timein);

it always returns the difference as 255, can anyone help me out on this?

 

[sao123]

it might be helpful if you post some actual code.

255, is the absolute value of an signed 8 bit space. it sounds like you have a type mismatch somewhere. What type is timein and timeout declared as?

 

[Ken g6]

And/or just do:

long timediff = labs((long)timeout - (long)timein);

But...if your values are in that format, won't 1400-1359 = 41?

And finally, why long? 2359 easily fits in an int.

 

[degibson]

Originally posted by: sao123
it might be helpful if you post some actual code.

Agreed.
Show us how timeout and timein are declared and initialized.

255, is the absolute value of an signed 8 bit space. ...

255 is the absolute value of an unsigned 8 bit space. ;-)

Originally posted by: Ken g6
And/or just do:

long timediff = labs((long)timeout - (long)timein);

But...if your values are in that format, won't 1400-1359 = 41?

Pay attention to this, OP. Its fairly common in C to represent times as 'seconds elapsed since the epoch' -- its not clear if the OP is doing this, however, as we don't see all of the code.