C :

#include<stdio.h>
int main()
{
    int num,result=0;
    
    scanf("%d",&num);
    while(num < 0)
        exit(0);
    while(num != 0)
    {
        result += (num%10);
        num = num / 10;
    }
    printf("%d\n",result);
}

C++ :

#include<iostream>
#include<cstring>
using namespace std;
int main(){
	
	int a[11];
	string s;
	memset(a,0,sizeof(a));
	
	cin>>s;
	
	int n=s.length();
	
	
	for(int i=0;i<n;i++){
		a[i]=s[i]-'0';
	}
	
	int sum=0;
	
	for(int i=0;i<n;i++)
	 	sum=sum+a[i];
	 	
	cout<<sum<<endl;
	
	
}

Python :

s=list(map(int,input()))
n=len(s)
m=0
for i in range(n):
    m=m+s[i]
print(m)