学习VC6.0时的练手程序。支持输入表达式的计算器，可以分步计算。比如3+2*Sin(32-5*8),开分步计算的情况下算一次是3+2*Sin(32-40)。-VC6.0 hand when learning to practice procedures. The calculator supports input expression can be calculated step by step. For example 3+2* Sin (32-5* 8), calculated step