C :

#include<stdio.h>
int main()
{
	int n,s=0,i=1,x;
	scanf("%d",&n);
	for(;i<=n;i++)
	{	x=i;
		do{
		if(x%10==1)s++;
		x=x/10;
		}while(x!=0);
	}
	printf("%d",s);
 	return 0;
}

C++ :

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

int main(){
	int i,g,s,b,q,n,c = 0;
	cin>>n;
	for(i = 1;i <= n;i++){
		g = i % 10;
		s = i / 10 % 10;
		b = i / 100 % 10;
		q = i / 1000;
		
		if(g == 1){
			c++;
		}
		
		if(s == 1){
			c++;
		}
		
		if(b == 1){
			c++;
		}
		
		if(q == 1){
			c++;
		}
	}
	
	cout<<c<<endl;
}

Python :

n = int(input())
c = 0
# 循环1~n
for i in range(1, n + 1):
    # 对每个1~n的数拆位,看有多少个1,c+=1
    while i > 0:
        s = i % 10
        if s == 1:
            c += 1
        i //= 10
print(c)