We can manipulate numbers by combining them with operators to form mathematical expressions, and by calling built-in functions to perform complex mathematical operations.
Basic arithmetic—addition, subtraction, multiplication, and division—is accomplished using the +, -, *, and / operators. Operators can be used with any numeric literals or data containers such as variables. Mathematical expressions are evaluated in the order determined by the precedence of the operators as shown in Table 5.1. For example, multiplication is performed before addition. All of these are legitimate uses of mathematical operators:
x = 3 * 5; // Assign the value 15 tox
x = 1 + 2 - 3 / 4; // Assign the value 2.25 tox
x = 56; y = 4 * 6 + x; // Assign the value 80 toy
y = x + (x * x) / x; // Assign the value 112 toy
To perform advanced math, we use the
built-in mathematical
functions of the Math
object. For example:
Math.abs(x) // Absolute value ofx
Math.min(x, y) // The smaller of the valuesx
andy
Math.pow(x, y) //x
raised to the powery
Math.round(x) //x
rounded to the nearest integer
The math functions return values that we use in expressions, just as
we use real numbers. For example, suppose we want to simulate a
six-sided die. We can use the
random( )
function to retrieve a random float between
and 1:
dieRoll = Math.random( );
Then we multiply that value by 6, giving us a float between and 5.999, to which we add 1:
dieRoll = dieRoll * 6 + 1; // Sets dieRoll
to a number between 1 and 6.999
Finally, we use the
floor(
)
function to round our number down to the closest
integer:
dieRoll = Math.floor(dieRoll); // Sets dieRoll
to a number
// between 1 and 6
Compressed into a single expression, our die roll calculation looks like this:
// Sets dieRoll
to a number between 1 and 6
dieRoll = Math.floor(Math.random( ) * 6 + 1);
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