CODEWITHSUNDEEP
objective-cnumbers
Pierre
Pierre

Reputation: 160

How to write negative number in obj C?

I´m trying to write a negative number like this: 

} else if ([newsCondition.temperature floatValue] == -7.0f) {

but that won´t trigger it and the negative symbol is black whilst the number is blue. How can I write the number so that it triggers when temperature isEqual to -7.0 degrees?

Upvotes: 1

Views: 1089

Answers (2)

occulus
occulus

Reputation: 17012

The way you've written your negative number (-7.0f) is correct.

As for your code not triggering: the floating point representation of numbers is not perfect, and you have to be aware of these issues when comparing floating point numbers to each other.

If you're wanting to compare two floating point numbers, you can use an 'epsilon' (i.e. acceptable error) for the comparison. This is basically checking if the numbers are close enough.

Simple naive example:

#define EPSILON 0.00001f

float x = 0.09f;
float y = 0.0901f;

if (abs(y - x) < EPSILON) {
    // close enough to be considered equal;
    // do something here
}

For more discussion, see http://floating-point-gui.de/errors/comparison/

Upvotes: 1

Shamsudheen TK
Shamsudheen TK

Reputation: 31311

Floating-point arithmetic is considered an esoteric subject by many people. This is rather surprising because floating-point is ubiquitous in computer systems. Almost every language has a floating-point datatype; computers from PCs to supercomputers have floating-point accelerators; most compilers will be called upon to compile floating-point algorithms from time to time; and virtually every operating system must respond to floating-point exceptions such as overflow. This paper presents a tutorial on those aspects of floating-point that have a direct impact on designers of computer systems. It begins with background on floating-point representation and rounding error, continues with a discussion of the IEEE floating-point standard, and concludes with numerous examples of how computer builders can better support floating-point.

From What Every Computer Scientist Should Know About Floating-Point Arithmetic

Upvotes: 0

Related Questions