本演示程序在vc++6.0环境用c语言编写，完成任意实数表达式的计算，并对表达式的错误预警，并能把表达式及结果以文件形式存储起来(This demo program is written in C language in the vc++6.0 environment. It completes the calculation of any real number expression, and the early warning of the expression error, and can store the expression and result in file form.)