喝汽水，1瓶汽水1元，2个空瓶可以换一瓶汽水，给20元，可以多少汽水。

这道题有两种喝法：1，可以借一个瓶盖 2，不可赊欠
1，可以赊欠一个瓶盖
20 => 10 => 5 => 2 => 1 => 1 => 1 （赊欠）

#include <stdio.h>
#include <stdlib.h>

int main(){
	int drink = 20;
	int cover = 20;
	int sum = 20;
	while (cover != 1){
		drink = cover;
		cover = drink / 2 + drink % 2;
		sum += drink / 2;
	}
	printf("%d \n", sum + 1);
	system("pause");
	return 0;
}

2，不可赊欠

#include <stdio.h>
#include <stdlib.h>

int main(){
	int drink = 20;
	int cover = 20;
	int sum = 20;
	while (cover != 1){
		drink = cover;
		cover = drink / 2 + drink % 2;
		sum += drink / 2;
	}
	printf("%d \n", sum);  //不可赊欠
	system("pause");
	return 0;
}

差异就在最后加上个1