中缀表达式转后缀表达式并计算后缀表达式

最新推荐文章于 2019-07-08 17:31:58 发布

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最新推荐文章于 2019-07-08 17:31:58 发布

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CC 4.0 BY-SA版权

原文链接：http://www.cnblogs.com/sdlwlxf/p/4971744.html

本文详细介绍了如何使用C++实现中缀表达式到后缀表达式的转换过程，包括栈的应用、操作符优先级的判断以及转换步骤的详细解释。

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

int computeSuffixExp(char expression[], size_t len)
{
    std::stack<int> dump;
    for (int i = 0; i < len; ++i)
    {
        if (isdigit(expression[i]))
        {
            dump.push(expression[i] - '0');
        }
        else
        {
            int num1 = dump.top();
            dump.pop();
            int num2 = dump.top();
            dump.pop();
            int num3;
            switch (expression[i])
            {
            case '+':
                num3 = num2 + num1;
                break;
            case '-':
                num3 = num2 - num1;
                break;
            case '*':
                num3 = num2 * num1;
                break;
            case '/':
                num3 = num2 / num1;
                break;
            }
            dump.push(num3);
        }
    }
    return dump.top();
}

// ( >>> *、- >>> +、-
void infixToSuffix(char exp[], char outExp[], int len)
{
    std::stack<char> symbols;
    std::string output;
    for (int i = 0; i < len; ++i)
    {
        char cur = exp[i];
        if (isdigit(cur))
            output.push_back(cur);
        else
        {
            if (symbols.size() == 0)
                symbols.push(cur);
            else
            {
                if (cur == '-' || cur == '+')
                {
                    char top = symbols.top();
                    while ((top == '*' || top == '/') && top != '(')
                    {
                        output.push_back(top);
                        symbols.pop();
                        top = symbols.top();
                    }
                    symbols.push(cur);
                }
                else if (cur == '(')
                {
                    char top = symbols.top();
                    while (top != '(')
                    {
                        output.push_back(top);
                        symbols.pop();
                        top = symbols.top();
                    }
                    symbols.push(cur);
                }
                else if (cur == ')')
                {
                    char top = symbols.top();
                    while (top != '(')
                    {
                        output.push_back(top);
                        symbols.pop();
                        top = symbols.top();
                    }
                    symbols.pop();
                }
                else
                    symbols.push(cur);
            }
        }
    }
    while (symbols.size() > 0)
    {
        output.push_back(symbols.top());
        symbols.pop();
    }
    strcpy_s(outExp, len, output.c_str());
}

int main() {
    char infix[] = { '(','(','4','+', '5',')', '*', '6', '+', '7',')' ,'/', '6'};
    char suffix[13];
    infixToSuffix(infix, suffix, 13);
    int res = computeSuffixExp(suffix, strlen(suffix));
    return 0;
}