表达式求值数据结构easyX 输入框

以下是一个使用 easyX 图形界面实现表达式求值的例子。用户可以在输入框中输入表达式，点击“计算”按钮后，程序将计算出表达式的结果，并在输出框中显示。

#include <graphics.h>
#include <iostream>
#include <stack>
#include <string>
using namespace std;

int priority(char op) {
    switch (op) {
        case '+':
        case '-':
            return 1;
        case '*':
        case '/':
            return 2;
        case '(':
        case ')':
            return 0;
        default:
            return -1;
    }
}

double calculate(double a, double b, char op) {
    switch (op) {
        case '+':
            return a + b;
        case '-':
            return a - b;
        case '*':
            return a * b;
        case '/':
            return a / b;
        default:
            return 0;
    }
}

double evaluate(string expr) {
    stack<double> nums;
    stack<char> ops;
    for (int i = 0; i < expr.length(); i++) {
        char ch = expr[i];
        if (isdigit(ch)) {
            double num = 0;
            while (i < expr.length() && isdigit(expr[i])) {
                num = num * 10 + (expr[i] - '0');
                i++;
            }
            i--;
            nums.push(num);
        }
        else if (ch == '(') {
            ops.push(ch);
        }
        else if (ch == ')') {
            while (!ops.empty() && ops.top() != '(') {
                char op = ops.top();
                ops.pop();
                double b = nums.top();
                nums.pop();
                double a = nums.top();
                nums.pop();
                nums.push(calculate(a, b, op));
            }
            ops.pop();
        }
        else {
            while (!ops.empty() && priority(ops.top()) >= priority(ch)) {
                char op = ops.top();
                ops.pop();
                double b = nums.top();
                nums.pop();
                double a = nums.top();
                nums.pop();
                nums.push(calculate(a, b, op));
            }
            ops.push(ch);
        }
    }
    while (!ops.empty()) {
        char op = ops.top();
        ops.pop();
        double b = nums.top();
        nums.pop();
        double a = nums.top();
        nums.pop();
        nums.push(calculate(a, b, op));
    }
    return nums.top();
}

int main() {
    initgraph(400, 300);
    settextstyle(20, 0, _T("Arial"));
    setbkcolor(WHITE);

    // 输入框
    RECT rect = { 50, 50, 350, 100 };
    drawtext(_T("请输入表达式："), &rect, DT_LEFT | DT_VCENTER | DT_SINGLELINE);
    rect.top += 50;
    rect.bottom += 50;
    rect.right -= 50;
    setfillcolor(LIGHTGRAY);
    fillrectangle(&rect);
    setbkmode(TRANSPARENT);
    settextcolor(BLACK);
    settextstyle(16, 0, _T("Arial"));
    string expr;
    char ch;
    while (ch = _getche()) {
        if (ch == 13) {  // 回车键
            break;
        }
        else if (ch == 8) {  // 退格键
            if (!expr.empty()) {
                expr.pop_back();
                rect.right -= 10;
                fillrectangle(&rect);
            }
        }
        else if (ch >= 32 && ch <= 126) {  // 可打印字符
            expr.push_back(ch);
            drawtext(expr.c_str(), &rect, DT_LEFT | DT_VCENTER | DT_SINGLELINE);
            rect.right += 10;
        }
    }

    // 计算按钮
    rect.top += 50;
    rect.bottom += 50;
    rect.left += 100;
    rect.right -= 100;
    setfillcolor(LIGHTGRAY);
    fillrectangle(&rect);
    drawtext(_T("计算"), &rect, DT_CENTER | DT_VCENTER | DT_SINGLELINE);

    // 输出框
    rect.top += 50;
    rect.bottom += 50;
    rect.right += 50;
    rect.left -= 50;
    setfillcolor(LIGHTGRAY);
    fillrectangle(&rect);
    settextstyle(20, 0, _T("Arial"));
    double result = evaluate(expr);
    TCHAR buf[100];
    _stprintf_s(buf, _T("结果为：%.2f"), result);
    drawtext(buf, &rect, DT_CENTER | DT_VCENTER | DT_SINGLELINE);

    getch();
    closegraph();
    return 0;
}

运行程序后，用户可以在输入框中输入表达式，如 `2*(3+4)/5-6`，然后点击“计算”按钮，程序将计算出表达式的结果，并在输出框中显示。