10以内数的四则运算表达式求值。利用堆栈的后进先出实现当运算符优先级较低的时候对操作数和运算符的出栈进行运算。-10 less than the number four operator expression is evaluated. The use of LIFO stack to achieve when the operator when a lower priority on the operand and operator of a stack to carry out comput