表达式是数据运算的基本形式。人们的书写习惯是中缀式，如：11+22*(7-4)/3。中缀式的计算按运算符的优先级及括号优先的原则，相同级别从左到右进行计算。表达式还有后缀式（如：22 7 4 - * 3 / 11 +）和前缀式（如：+ 11 / * 22 – 7 4 3）。后缀表达式和前缀表达式中没有括号，给计算带来方便。如后缀式计算时按运算符出现的先后进行计算。本设计的主要任务是进行表达式形式的转换及不同形式的表达式计算。-Expression is the basic form of data operation. People' s writing habits are infix type, such as: 11+22* (7-4)/3. Infix calculator by operator precedence and the principle of priority in parentheses, are calculated the same level from left to right. There postfix expression (such as: 2274--* 3/11+) and prefix-style (such as:+ 11 /* 22--743). Suffix and prefix expressions expressions without parentheses, to the calculation of convenience. Calculated as the suffix appears, press operators have calculated. The design of the main tasks of the expression in the form of transformation and different forms of expression evaluation.