Not all numbers are integers. Therefore, Objective-C lets you define floating-point values—numbers with a fractional portion. There are two basic types—float and double.
Floating-point values do not follow the rules of integer division—that is, dividing by floating-point values produces floating-point results.
In certain programming languages (Java comes to mind) the float type is almost never used. In Objective-C, it is the more commonly used of the two—both for practical and memory reasons.
A floating point number must contain a decimal portion, but you can omit digits before or after the decimal point—obviously, not both. The entire number ca be prefixed by a negative sign. Therefore, 3., 1.8, .295, and -.59 are all valid floating point numbers. To display floats in an NSLog call, use %f.
As you may recall from a high-school math class, scientific notation is a method of writing absurdly large or small numbers. It takes the form 5.925×102, where the general notation is of a floating-point value followed by a multiplication, a number (generally a power of 10), and an exponent. This number is written in code with the form 5.925e4. The e, formally known as the mantissa, can be written as a capital or lowercase. The mantissa can be either positive or negative; a negative value, such as 2.25e-3, would correspond to a value of 2.25×10-3, or 0.00225.
To display scientific notation, use %e. Alternatively, you can use %g to have NSLog decide whether to display the usual value or the scientific notation—if the exponent is less than -4 or greater than 5, the scientific notation is used; otherwise, the standard floating point notation is used.
A double value is a more precise float value—the former stores twice as many digits, and on most systems it uses 64 bits.
Like Java, all floating point constants in Objective-C are double. To force a float, append either f or F to the end of the floating point value. Unlike Java, however, floats are used as a general data type for floating-point variables, due to the fact that they require less memory. The distinction is that of constants versus that of variables.
The same format specifiers apply to doubles, as well as scientific notation.
This post is part of the Learn Objective-C in 24 Days course.
Author: Feifan Zhou