中缀转后缀及表达式求值

来源：互联网发布：徐小明交易师软件编辑：程序博客网时间：2024/05/21 10:10
代码。。。。
/*    参考:http://www.nowamagic.net/librarys/veda/detail/2306         http://blog.csdn.net/geekcoder/article/details/6829386         http://blog.csdn.net/mvpsendoh/article/details/6440559         虽说是参考，可是受作者思路影响，里面相同的地方还是太多了= =。*/#include <iostream>#include <stack>#include <ctype.h>#include <stdlib.h>#include <math.h>#define ENDCHAR '#'using namespace std;//中缀转后缀部分int isOperator(char c){    switch(c)    {        case '+':        case '-':        case '*':        case '/':        case '%':        case '^':            return 1;                default:            return 0;    }}int priority(char c){    switch(c)    {        case ENDCHAR:        case '(':            return 0;        case '+':        case '-':            return 1;        case '%'://坑爹了。。学了这么久，今天终于知道求模跟乘除是同一优先级        case '*':        case '/':            return 2;        case '^':            return 4;        default:            cout << "Invalid Operator!: '" << c << "'" << endl;            exit(1);    }}void popAll(stack<char>&stk, char postfix[], int postIndex){    while(stk.size() != 0)    {        postfix[postIndex++] = stk.top();        stk.pop();    }    postfix[--postIndex] = '\0'; //在'#'处插入结束符}void infix2postfix(char infix[], char postfix[]){    int inIndex = 0, postIndex = 0;    stack<char>operators;    operators.push(ENDCHAR);//压入ENDCHAR避免后面操作到空栈而出错    while(infix[inIndex])    {        if(isdigit(infix[inIndex]) || infix[inIndex] == '.') //数字直接输出到postfix中        {            postfix[postIndex++] = infix[inIndex];        }        else if(infix[inIndex] == '(')        {            //'(' 入栈            operators.push(infix[inIndex]);        }        else if(infix[inIndex] == ')')   //括号与运算符分开处理        {        /*            当当前符号为')'            则依次弹出栈中符号直至遇到'('        */            while(operators.top() != '(')            {                postfix[postIndex++] = operators.top();                operators.pop();            }            operators.pop();  //弹出'('        }        else if(isOperator(infix[inIndex]))        {        /*            将当前操作符与栈顶操作符比较            若小于等于栈顶操作符            则将栈顶操作符弹出直至当前操作符大于栈顶操作符            最后将当前操作符入栈        */            postfix[postIndex++] = ' ';  //隔开操作数            while(priority(infix[inIndex]) <= priority(operators.top()))            {                postfix[postIndex++] = operators.top();                operators.pop();            }            operators.push(infix[inIndex]);        }        ++inIndex;    }    popAll(operators, postfix, postIndex);//全部操作符出栈}//表达式求值部分double calc(double num1, double num2, char op){    switch(op)    {        case '+':return num1 + num2;        case '-':return num1 - num2;        case '*':return num1 * num2;        case '/':return num1 / num2;        case '%':return fmod(num1, num2);        case '^':return pow(num1, num2);        default:            exit(1);    }}double readNumber(char **string){    double intNumber = 0;    double floatNumber = 0;    int times = 1;    while(isdigit(**string))    {        intNumber = intNumber * 10 + **string - '0';        ++*string;    }    if(**string == '.')    {        ++*string;        while(isdigit(**string))        {            floatNumber = floatNumber + (**string - '0') * pow(0.1, times);            ++*string;        }    }    return intNumber + floatNumber;}double calcPostfix(char postfix[]){    double num1, num2;    stack<double>numbers;    while(*postfix)    {        if(isdigit(*postfix))        {            numbers.push(readNumber(&postfix));//读取数字        }        else if(isOperator(*postfix))        {           /*            取得2操作数            执行当前运算并将结果入栈        */            num2 = numbers.top();            numbers.pop();            num1 = numbers.top();            numbers.pop();            numbers.push(calc(num1, num2, *postfix++));        }        else if(isspace(*postfix))        {            ++postfix; //跳过空格        }    }    return numbers.top();}int main(){    char infix[100] = "", postfix[100] = "";    while(1)    {        cout << "Input:";        cin >> infix;        infix2postfix(infix, postfix);        cout << "Postfix:" << postfix << endl;        cout << "Value:" << calcPostfix(postfix) << endl;    }    return 0;}
运行截图。。。
总结。。。
终于知道%*/是同一优先级了。。。。
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