题解 | #计算器的改良# C++

#include <iostream>
#include <cstdio>
#include <cmath>
#include <string>
using namespace std;

int main(){
    // x是系数；v是值；等号左边equal为1，右边为-1；sign记录符号位；total记录系数或值的数字；
    int x = 0, v = 0, equal = 1, sign = 1, total = 0;
    // t记录未知数
    char c, t;
    while (cin >> c) {
        // 遇到+号，值移到右边，符号位记为1，total归0
        if (c == '+') {
            v -= total * sign * equal;
            sign = 1;
            total = 0;
        // 遇到-号，值移到右边，符号位记为-1，total归0
        }else if (c == '-') {
            v -= total * sign * equal;
            sign = -1;
            total = 0;
        // 遇到=号，值移到右边，符号位记为1，total归0，equal记为-1
        }else if (c == '=') {
            v -= total * sign * equal;
            sign = 1;
            equal = -1;
            total = 0;
        // 如果total为0系数为1，t记录未知数，将系数移项至左边，total归0
        }else if (isalpha(c)) {
            if (total == 0) x += 1;
            t = c;
            x += total * sign * equal;
            total = 0;
        // 记录系数或值
        }else {
            total = total * 10 + (c - '0');
        }
    }
    // 计算最后一个值
    v -= total * sign * equal;
    printf("%c=%.3f\n", t, (double)v/x);
    return 0;
}