后缀表达式求值算法

stack operands;  //运算数栈
while(没到表达式尾)
{scanf("一个运算对象op");if(op is 运算数)operands.push(op);else if(op is 运算符){operand_right = operands.pop();operand_left = operands.pop();result = operand_left op operand_right;operands.push(result);}else{printf("Suffix expression is invalid !");}
}
if(operands.size() == 1)return operands.top();
elseprintf("Suffix expression is invalid!");

前缀表达式求值算法

算法一：从表达式尾部开始处理(从右至左)

伪代码描述：

stack operands;   //运算数栈
while(没到达表达式首)
{scanf("一个运算对象op");if(op is Operand)operands.push(op);else if(op is Operator){operand_left = operands.pop();operand_right = operands.pop();result = operand_left op operand_right;operands.push(result);}else{printf("Prefix expression is invalid!");}
}
if(operands.size() == 1)
{return operands.top();
}
elseprintf("Prefix expression is invalid!");

算法二：从表达式首部开始处理(从左至右)

stack operations;  //运算对象栈，元素既可以是云算法，也可以是运算数
while(没到表达式尾)
{scanf("一个运算对象op");if(op is Operator){operations.push(op);}else if(op is Operand){if(operations.top() is Operator){operations.push(op);}else{while(operations.top() is Operand){operand_right = op;operand_left = operations.pop();operator = operations.pop();op = operand_left operator operand_right;}operations.push(op);}}else{printf("Prefix expression is invalid!");}
}
if(operations.size() == 1)return operations.top();
elseprintf("Prefix expression is invalid!");

中缀表达式转换为后缀表达式算法

stack operators;   //运算符栈
while(没到表达式尾)
{scanf("一个运算对象op");if(op is Operand){printf(op);}else if(op is Operator){if(op 优先级大于 operator.top() && op is not 右括号)operator.push(op);else if(op is 右括号){do{tmp = operators.pop();if(tmp is not 对应左括号){printf(tmp);}else{break;}if(operators.empty()){printf("Infix expression is invalid!");}}while(1);}else{do{tmp = operators.pop();printf(tmp);}while(op 优先级小于 operators.top());operators.push(op);}}else{printf("Infix expression is invalid!");}
}
while(!operators.empty())
{tmp = operators.pop();printf(tmp);
}

中缀表达式转换为前缀表达式算法

从表达式尾部开始处理

stack operators;  //运算符栈stack operations;  //运算对象栈，元素既可以是运算符，也可以是运算数while (没到表达式首){scanf("一个运算对象op");if (op is Operand){operations.push(op);}else if (op is Operator){if (op 优先级大于 operators.top() && op is not 左括号)operators.push(op);else if (op is 左括号){do{tmp = operators.pop();if (tmp is not 对应右括号){operations.push(tmp);}else{break;}if (operators.empty()){printf("Infix expression is invalid!");}}while(1);}else{do{tmp = operators.pop();operations.push(tmp);}while(op 优先级小于 operators.top());operators.push(op);}}else{printf("Infix expression is invalid!");}}while(!operators.empty()){tmp = operators.pop();operations.push(tmp);}while(!operations.empty()){tmp = operations.pop();printf(tmp);}