C ++ Stack StringStream函数返回整数vs ASCII

Question

#include <iostream>
#include <string>
#include <stack>
#include <sstream>

using namespace std;

stack<int>aStack;
stack<int>operand1;
stack<int>operand2;
stringstream postfix;

stringstream &postfixExp(string ch)
{
  for(int i =0; i< ch.length(); i++)
  {
      if(ch[i] == '1' || ch[i] == '2' || ch[i] == '3' || ch[i] == '4' || ch[i] == '5' || ch[i] == '6' || ch[i] == '7' || ch[i] == '8' || ch[i] == '9' || ch[i] == '0' )
      {
          aStack.push(ch[i]);
      }

      else if(ch[i] == '+')
      {
        operand1.push(aStack.top());
        aStack.pop();

        operand2.push(aStack.top());
        aStack.pop();

        int x = operand1.top() - 48;
        int y = operand2.top() - 48;
        int result = x + y;

        aStack.push(result);
      }

      else if(ch[i] == '*')
      {
        operand1.push(aStack.top());
        aStack.pop();

        operand2.push(aStack.top());
        aStack.pop();

        int x = operand1.top() - 48;
        int y = operand2.top() - 48;
        int result = x * y;

        aStack.push(result);
      }
  }


  postfix << aStack.top();
  return postfix;

}


int main()
{
  string postfix = "32+2*";

  stringstream * result = &postfixExp(postfix);
  cout << result-> str() ;

  return 0;
}

嗨，有人知道我上面的代码有什么问题吗？ 我的程序应返回后缀表示法的值。 我输入“ 32 + 2 *”作为后缀表示法，它应该返回10。显然出了点问题，它返回-86代替

我想错误来自此特定代码

else if(ch[i] == '*')
      {
        operand1.push(aStack.top());
        aStack.pop();

        operand2.push(aStack.top());
        aStack.pop();

        int x = operand1.top() - 48;
        int y = operand2.top() - 48;
        int result = x * y;

        aStack.push(result);
      }

从那里，我显示了操作数2，它显示的是-43而不是7（来自上一个加法运算符“ 34+”的推导）

请让我知道哪一部分是错误的，为什么我的操作数2的值不为7。

谢谢

Answer 1

在将字符压入堆栈之前，将其转换为整数。 在我看来，您的编译器应该已经对此发出警告。 尝试提高警告级别。

aStack.push(ch[i]);

变

aStack.push(ch[i] - '0'); // '0' is 48

还要注意，您可以使用<cctype> isdigit ，而不是手动将ch[i]与每个数字进行比较。

Answer 2

  if(ch[i] == '1' || ch[i] == '2' || ch[i] == '3' || ch[i] == '4' || ch[i] == '5' || ch[i] == '6' || ch[i] == '7' || ch[i] == '8' || ch[i] == '9' || ch[i] == '0' )
  {
      aStack.push(ch[i]);
  }

应该是：

  if(ch[i] == '1' || ch[i] == '2' || ch[i] == '3' || ch[i] == '4' || ch[i] == '5' || ch[i] == '6' || ch[i] == '7' || ch[i] == '8' || ch[i] == '9' || ch[i] == '0' )
  {
      aStack.push(ch[i] - '0');
  }

摆脱其他- 48损坏了。

Answer 3

问题如下

  else if(ch[i] == '+')
  {
    operand1.push(aStack.top());
    aStack.pop();

    operand2.push(aStack.top());
    aStack.pop();

    int x = operand1.top() - 48;
    int y = operand2.top() - 48;
    int result = x + y;

    aStack.push(result + 48);
   }

这将使其变为10。您还需要更改第二个aStack.push（result）。