C写的计算器，支持四则运算、括号、百分号、乘幂、三角函数、反三角函数、常量π、e，支持自定义变量，详细出错提示信息。代码有详细注释。-C calculator written in support of four operations, brackets, percent sign, take power, trigonometric functions, inverse trigonometric functions, constants, π, e, support custom variables, error messages for details. Detailed code comments.