C++ 算术表达式求值代码 |21xrx.com

C++ 算术表达式求值代码

2023-06-30 20:12:23 深夜i 16 0

C++ 算术表达式求值代码计算器

本文将介绍一个用C++编写的算术表达式求值代码，该代码可以对基本的算术表达式进行求值，包括加减乘除和括号。下面是代码的实现过程：

首先，我们使用栈来存储数字和运算符。具体步骤如下：

1. 遍历整个表达式，从左到右逐个读取字符。

2. 如果读取的是数字，则将其入栈。

3. 如果读取的是运算符，则从栈中弹出两个数字，计算出它们的结果，再将结果入栈。

4. 如果读取的是左括号，则将其入栈。

5. 如果读取的是右括号，则从栈中弹出数字和运算符，直到遇到左括号，计算出中间结果，再将结果入栈。

6. 当遍历完整个表达式时，栈中剩余的数字和运算符一定可以计算出最终结果。

下面是完整的C++代码实现：

#include <iostream>
#include <stack>
#include <string>
using namespace std;
int evaluate(string expression) {
  stack<int> numbers;
  stack<char> operators;
  int number = 0;
  for (int i = 0; i < expression.length(); i++) {
    char current = expression[i];
    if (isdigit(current)) {
      number = number * 10 + (current - '0');
    }
    else if (current == '+' || current == '-' || current == '*' || current == '/') {
      numbers.push(number);
      number = 0;
      while (!operators.empty() && ((current != '*' && current != '/') || (operators.top() == '*' || operators.top() == '/'))) {
        int operand2 = numbers.top();
        numbers.pop();
        int operand1 = numbers.top();
        numbers.pop();
        char op = operators.top();
        operators.pop();
        int result;
        if (op == '+') {
          result = operand1 + operand2;
        }
        else if (op == '-')
          result = operand1 - operand2;
        
        else if (op == '*') {
          result = operand1 * operand2;
        }
        else
          result = operand1 / operand2;
        
        numbers.push(result);
      }
      operators.push(current);
    }
    else if (current == '(') {
      operators.push(current);
    }
    else if (current == ')') {
      while (operators.top() != '(') {
        int operand2 = numbers.top();
        numbers.pop();
        int operand1 = numbers.top();
        numbers.pop();
        char op = operators.top();
        operators.pop();
        int result;
        if (op == '+') {
          result = operand1 + operand2;
        }
        else if (op == '-')
          result = operand1 - operand2;
        
        else if (op == '*') {
          result = operand1 * operand2;
        }
        else
          result = operand1 / operand2;
        
        numbers.push(result);
      }
      operators.pop();
    }
  }
  numbers.push(number);
  while (!operators.empty()) {
    int operand2 = numbers.top();
    numbers.pop();
    int operand1 = numbers.top();
    numbers.pop();
    char op = operators.top();
    operators.pop();
    int result;
    if (op == '+') {
      result = operand1 + operand2;
    }
    else if (op == '-')
      result = operand1 - operand2;
    
    else if (op == '*') {
      result = operand1 * operand2;
    }
    else
      result = operand1 / operand2;
    
    numbers.push(result);
  }
  return numbers.top();
}
int main() {
  string expression = "1+2*3+(4-2)/2";
  cout << evaluate(expression) << endl;
  return 0;
}

以上就是C++算术表达式求值代码的实现过程和完整代码示例。通过这个代码，我们可以轻松地对基本的算术表达式进行求值，实现计算器等功能。

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