功能强大的计算器，采用仿C语言表达式语法 并且给出表达式的逆波兰表达式，支持二十余种函数运算，程序经测试成功-powerful calculator, using fake C language syntax expression and expression is the inverse Poland expression, I support 20 species of Operational functions, procedures have been tested successful

计算器，仿windows计算器的。学生开发的代码，有bug请谅解！-Calculator, fake windows calculator. Students to develop the code, a bug, please understanding!