Arithmetic expressions

Whenever gd1 or gd1.pp encounter the string eval(, the matching closing brace is searched and the string inside the enclosing braces is interpreted as an arithmetic expression. The value of the expression is transformed to a string and substituted for eval(expression).
Example

 echo (2*3)      # this outputs "(2*3)"
 echo eval(2*3)  # this outputs "6"

The arithmetic expression may contain the arithmetic operators +,-,*,/,**,%. In addition to that, the boolean operators ==,!=,<,>,<=,>= are handled. The result of applying a boolean operator is an integer 0 or 1. Zero stands for false, and 1 for true.

The functions cos(), sin(), atan() are recognised and evaluated.

In every context, where a number is required as a parameter, an arithmetic expression can be used. In these contexts, enclosing the expression in eval() is not required.