将中缀转换为后缀：无法识别堆栈错误

Question

我是一名初学者，使用堆栈，因此我一直在尝试对它进行不同的练习。我试图转换中缀 - >后缀。 Xcode的调试器说“类模板的使用 'stack'requires模板参数'。这是我的代码。

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

using namespace std; 


bool IsOperand(char ch) 
{ 
    if ((ch >= '0' && ch <= '9') || (ch >= 'A' && ch <= 'Z') || (ch >= 'a' && ch <= 'z')) { 
     return true; 
    } 
    return false; 
} 

bool IsOperator(char C) 
{ 
    if (C == '+' || C == '-' || C == '*' || C == '/' || C == '^') { 
     return true; 
    } 
    return false; 
} 
bool IsLeftParenthesis(char ch) 
{ 
    if (ch == '(') { 
     return true; 
    } 
    return false; 
} 

bool IsRightParenthesis(char ch) 
{ 
    if (ch == ')') { 
     return true; 
    } 
    return false; 
} 

bool Flag(char ch) 
{ 
    if (!IsOperand(ch) || !IsOperator(ch) || !IsLeftParenthesis(ch) || !IsRightParenthesis(ch)) { 
     return false; 
    } 
    return true; 
} 

int IsRightAssociative(char op) 
{ 
    if (op == '^') { 
     return true; 
    } 
    return false; 
} 
int GetOperatorWeight(char op) 
{ 
    int weight = -1; 
    switch (op) { 
     case '+': 
     case '-': 
      weight = 1; 
      break; 
     case '*': 
     case '/': 
      weight = 2; 
      break; 
     case '^': 
      weight = 3; 
      break; 
    } 
    return weight; 
} 

bool HasHigherPrecedence(char op1, char op2) 
{ 
    int op1Weight = GetOperatorWeight(op1); 
    int op2Weight = GetOperatorWeight(op2); 
    // If operators have equal precedence, return true if they are left associative. 
    // BUT REMEMBER...return false, if right associative. 
    // if operator is left-associative, left one should be given priority. 
    if (op1Weight == op2Weight) { 
     if (IsRightAssociative(op1)) { 
      return false; 
     } 
     else { 
      return true; 
     } 
    } 
    return op1Weight > op2Weight ? true : false; 
} 

string InfixToPostfix(string expression) 
{ 

    stack S; 
    string postfix = ""; 
    for (auto& elem : expression) { 
     if (Flag(elem)) { 
      continue; 
     } 
     // If character is operator, pop two elements from stack, perform operation and push the result back. 
     else if (IsOperator(elem)) { 
      while (!S.empty() && S.top() != '(' && HasHigherPrecedence(S.top(), elem)) { 
       postfix += S.top(); 
       S.pop(); 
      } 
      S.push(elem); 
     } 
     else if (IsOperand(elem)) { 
      postfix += elem; 
     } 
     else if (elem == '(') { 
      S.push(elem); 
     } 
     else if (elem == ')') { 
      while (!S.empty() && S.top() != '(') { 
       postfix += S.top(); 
       S.pop(); 
      } 
      S.pop(); 
     } 
    } 

    while (!S.empty()) { 
     postfix += S.top(); 
     S.pop(); 
    } 

    return postfix; 
} 

int main() 
{ 
    // std::string expression = "54/(5^2)+(6^2^3)"; 
    std::string expression = "A+(BC-(D/E^F)G)H"; 
    std::string postfix = InfixToPostfix(expression); 
    std::cout << "Output = " << postfix << "\n"; 
} 

这里specificially在错误发生的情况。

string InfixToPostfix(string expression) 
{ 

    stack S; 

它说

Stack S - >使用类模板'stack'requires template arguments'

Answer 1

栈是一个容器，你需要指定像容器的类型：

stack <int> S; 

或在你情况下，它的char堆栈：

stack <char> S;