View Code of Problem 101

#include <stdio.h>
#include <string.h>
int main()
{
	char str[100],str1[100];
	while(scanf("%s",&str) != EOF){
		int len = strlen(str);
		int i;
		int k = 0;
		int sum = 0;
		for(i = len-1;i >= 0;i --){
			if(str[i] >= '0'&&str[i] <= '9'){
				sum++;
				str1[k] = str[i];
				k++;
				if(sum == 3){
					str1[k] = ',';
					sum = 0;
					k++;
				}
			}
		}
		for(i = k-1;i >= 0;i--){
			printf("%c",str1[i]);
		}
		printf("\n");
	}
	return 0;
}