View Code of Problem 101

#include<stdio.h>
#include<string.h>
int main(){
    char s1[100];
    char s2[100];
    int i;
    while(scanf("%s",s1)!=EOF){
        int len =strlen(s1);
        int k=0,count=0;
        for(i=len-1;i>=0;i--){
            if(s1[i]!=','){
                s2[k++]=s1[i];
                count++;
                if(count%3==0&&i!=0){
                    s2[k++]=',';
                }
            }
        }
        for(i=k-1;i>=0;i--){
            printf("%c",s2[i]);
        }
        printf("\n");
    }
}