OJ_计算不带括号的表达式

题干

在这里插入图片描述

C++实现

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stack>
#include <string>
#include <map>
using namespace std;int main() {char str[1000] = { 0 };map<char, int> priority = {{'\0',0},{'+',1},{'-',1},{'*',2},{'/',2}};while (scanf("%s", str) != EOF) {string numStr = "";stack<char> opStack;stack<double> numStack;for (int i = 0; ; i++){if (str[i] >= '0' && str[i] <= '9') {numStr.push_back(str[i]);}else {double num = stod(numStr);numStr = "";numStack.push(num);//什么时候弹栈：符号栈非空&&新运算符优先级不超过栈顶优先级while (!opStack.empty() && priority[str[i]] <= priority[opStack.top()]) {double num1 = numStack.top();numStack.pop();double num2 = numStack.top();numStack.pop();char curOp = opStack.top();opStack.pop();if (curOp == '+') {numStack.push(num2 + num1);}else if (curOp == '-') {numStack.push(num2 - num1);}else if (curOp == '*') {numStack.push(num2 * num1);}else if (curOp == '/') {numStack.push(num2 / num1);}}//此时符号栈为空，或新运算符优先级高于栈顶if (str[i] == '\0') {printf("%d\n",(int)numStack.top());break;}else {opStack.push(str[i]);}}}}return 0;
}