参考方法：

#include<stdio.h>

//求a的b次方函数
unsigned ppow(unsigned a, unsigned b) {
    unsigned cc = 1;
    while (b) {
        cc*=a;
        b--;
    }
    return cc;
}
int main()
{
    unsigned long long n = 0;
    unsigned  i, k=0, count = 0;
    printf("请输入2进制数：");
    
    scanf_s("%lld", &n);          //用scanf（）在Visual Studio 2019 会警告返回值被忽略
    while (n) {
        i = n % 10;                //这个说错了，2和10都可以，用10会比较好
        if (i) {                  //判断i是否为0
            count += ppow(2, k);
        }
        k++;                      //k做为2的次方数，每次n /= 10 就+1
        n /= 10;
    }
    printf(" 转成10进制= %d",count);
    return 0;
}