题解 | #添加逗号#

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>


int main()
{
	long long a = 0;
	scanf("%lld",&a);
	int tmp = a;
	char arr[100] = { 0 };
	int count = 0;
	while (tmp)
	{
		count++;
		tmp = tmp / 10;
    }
	int count1 = count;
	int i = 0;
    int j = 1;
	for ( i = 0; count ; i++)
	{
		arr[i] = a % 10+48;
		if ((j) % 3 == 0&&a>10)
		{
			arr[i + 1] = ','; 
			i++;	
			count1++;
		}
		j++;
		count--;
		a = a / 10;
	}
	arr[i] = '\0';
	for (int j = count1-1; j>=0; j--)
	{
		printf("%c", arr[j]);
	}
	return 0;
}