#include <bits/stdc++.h>
using namespace std;

int main(){
    string a;
    cin>>a;
    int count=0;
    for(int i=0;i<a.length();i++){
        if(a[i]=='1'){
            count++;
        }
    }
    cout<<count;
}

C :

#include <stdio.h>
char a[9];
int t, i;
int main(void) {
    scanf("%s", &a);
    for (i = 0; i < 8; i++) {
        t += a[i] == '1';
    }
    printf("%d", t);
    return 0;
}

C++ :

#include<iostream>
#include<cmath>
using namespace std;
int main()
{
    string a;
    cin>>a;
    int c=0;
    for(int i=0;i<a.size();i++)
    {
        if(a[i]=='1')
            c++;//判断是不是一，如果是的话计数器++

    }
    cout<<c;
    return 0;
}

Python :

# coding=utf-8
a = input()
t = 0
for i in range(0, 8) :
    t = t + int(a[i] is '1')
print(t)