Question

即时学习c ++，我坚持理解某些代码行。

bool IsOperator(char C)
{
if(C == '+' || C == '-' || C == '*' || C == '/' || C== '$')
    return true;

return false;
}

如果字符串中的char是运算符，程序我试图理解扫描。如果是，请给他一个号码。 Inflix到postflix是这里的问题。

int IsRightAssociative(char op)
{
    if(op == '$') return true;
return false;
}

这是我无法理解的，如果我写的话程序找到'$'字符（（3 + 2）* 3-5）* 2 ??

我会附上整个代码以便更好地理解

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

using namespace std;

    // Function to convert Infix expression to postfix 
    string InfixToPostfix(string expression);

// Function to verify whether an operator has higher precedence over other
int HasHigherPrecedence(char operator1, char operator2);

// Function to verify whether a character is operator symbol or not. 
bool IsOperator(char C);

// Function to verify whether a character is alphanumeric chanaract (letter or numeric digit) or not. 
bool IsOperand(char C);

int main() 
{
string expression; 
cout<<"Enter Infix Expression \n";
getline(cin,expression);
string postfix = InfixToPostfix(expression);
cout<<"Output = "<<postfix<<"\n";
}

// Function to evaluate Postfix expression and return output
string InfixToPostfix(string expression)
{
// Declaring a Stack from Standard template library in C++. 
stack<char> S;
string postfix = ""; // Initialize postfix as empty string.
for(int i = 0;i< expression.length();i++) {

    // Scanning each character from left. 
    // If character is a delimitter, move on. 
    if(expression[i] == ' ' || expression[i] == ',') continue; 

    // If character is operator, pop two elements from stack, perform operation and push the result back. 
    else if(IsOperator(expression[i])) 
    {
        while(!S.empty() && S.top() != '(' && HasHigherPrecedence(S.top(),expression[i]))
        {
            postfix+= S.top();
            S.pop();
        }
        S.push(expression[i]);
    }
    // Else if character is an operand
    else if(IsOperand(expression[i]))
    {
        postfix +=expression[i];
    }

    else if (expression[i] == '(') 
    {
        S.push(expression[i]);
    }

    else if(expression[i] == ')') 
    {
        while(!S.empty() && S.top() !=  '(') {
            postfix += S.top();
            S.pop();
        }
        S.pop();
    }
}

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

return postfix;
}

// Function to verify whether a character is english letter or numeric     digit. 
// We are assuming in this solution that operand will be a single character
bool IsOperand(char C) 
{
if(C >= '0' && C <= '9') return true;
if(C >= 'a' && C <= 'z') return true;
if(C >= 'A' && C <= 'Z') return true;
return false;
}

// Function to verify whether a character is operator symbol or not. 
bool IsOperator(char C)
{
if(C == '+' || C == '-' || C == '*' || C == '/' || C== '$')
    return true;

return false;
}

// Function to verify whether an operator is right associative or not. 
int IsRightAssociative(char op)
{
if(op == '$') return true;
return false;
}

// Function to get weight of an operator. An operator with higher weight     will have higher precedence. 
int GetOperatorWeight(char op)
{
int weight = -1; 
switch(op)
{
case '+':
case '-':
    weight = 1;
case '*':
case '/':
    weight = 2;
case '$':
    weight = 3;
}
return weight;
}

// Function to perform an operation and return output. 
int 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. 
// 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;
}

所以，如果有人可以提供帮助，我将非常高兴:(。

如果字符串中的字符是某些符号，那么“$”是什么意思？

0 个答案: