计算机补码能够减法转加法的原因

可以想一下这道题（这里样例的二进制是补码）

我的代码

一些其他思路（特别是思路三，想想为啥）

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

int main() {
    char n = 0;
    int power = 30, k = 0, ans = 0;
    cin >> n;
    char m = n;  // 用m存补码的符号位
    if (m == '1') {
        // 符号位为负
        for (int i = 1; i <= 31; i++) {
            cin >> n;
            if (n == '1')
                k = 0;
            else
                k = 1;
            ans += k * pow(2, power);
            power = power - 1;
        }
        cout << (-ans - 1) << endl;
    } else {
        // 符号位为正
        for (int i = 1; i <= 31; i++) {
            cin >> n;
            if (n == '1') ans = ans + pow(2, power);
            power = power - 1;
        }
        cout << ans << endl;
    }
    return 0;
}

#include <stdio.h>
#include <string.h>

int binaryToDecimal(char* sequence) {
    int length = strlen(sequence);
    int num = 0;
    int isNegative = (sequence[0] == '1');
    for (int i = 1; i < length; i++) {
        num = (num << 1) + (sequence[i] - '0');
    }
    if (isNegative) {
        num = num - (1 << (length - 1));
    }
    return num;
}

int main() {
    char sequence[33];
    scanf("%s", sequence);
    int num = binaryToDecimal(sequence);
    printf("%d", num);
    return 0;
}