View Code of Problem 101

#include <stdio.h>
#include <stdlib.h>
#include<ctype.h>
#include<string.h>
#include<math.h>
#include<stdbool.h>
int main()
{
	int i, j, n;
	char a[20], b[20];
	while (gets(a))
	{
		n = 0;
		for (i = strlen(a) - 1, j = 0; i >= 0; i--)
		{
			if(isalnum(a[i]))
			{
				
				if (n % 3 == 0&&n!=0)
					b[j++] = ',';
				n++;
				b[j++] = a[i];
				
			}
			
		}
		for (i = j - 1; i >= 0; i--)
		{
			
			 printf("%c", b[i]);


		}
		printf("\n");
	}
	return 0;
}