Learning the iOS 4 SDK for JavaScript Programmers

Math Object Equivalents in C

The core JavaScript language has a static Math object, which features a number of methods and properties that act as constants. For example, if you want to determine the next lesser integer for a floating-point value, use the floor() method of the static Math object, as follows:

var floorValue = Math.floor(myValue);

The C language doesn’t have a dedicated object of that type. Instead, it implements a series of functions, which you can call directly in your statements. For example:

double floorValue = floor(myValue);

Table 7-3 lists the JavaScript Math object functions and the corresponding C functions. The standard C language offers far more variations of these functions (in the math.h and stdlib.h libraries automatically incorporated into every iOS app), offering differing levels of precision. For Table 7-3, I have chosen the versions that return values of the double data type. Also pay special attention to the required data type of values passed as arguments to the C functions.

Table 7-3. Math functions comparisons

JavaScript	Description	C/Objective-C
Math.abs(x)	Absolute value	double fabs(double x);
Math.acos(x)	Arc cosine	double acos(double x);
Math.asin(x)	Arc sine	double asin(double x);
Math.atan(x)	Arc tangent	double atan(double x);
Math.atan2(x, y)	Angle of polar coordinates	double atan2(double y, double x);
Math.ceil(x)	Next greater integer	double ceil(double x);
Math.cos(x)	Cosine	double cos(double x);
Math.exp(x)	Euler’s constant to xth power	double exp(double x);
Math.floor(x) ...