北大 acm 2521 How much did the businessman lose 解题报告

Time Limit: 1000MS Memory Limit: 65536K Total Submissions: 6719 Accepted: 4601

Description

Businessmen, of course, can make much money. However, sometimes, they would lose money in trading. For example, Jame, a businessman, brought in some goods each cost him 40 yuan and he decided to sell at the price of 70 yuan. Then a customer came to buy one, gave Jame 100 yuan, and of course got back 30 yuan. You may said, “Jame earned 30 yuan.” But unfortunately, Jame found the 100 yuan from the customer was fake. What a poor man! In this case Jame lost 70 yuan (40 (the goods price) + 30 (the money paid back to the customer)).

Now your task is to calculate how much Jame would lose in this kind of trade. Of course in this case, sometimes Jame may still earn.

Input

The input consists of several instances. Each instance contains four integers N, M, P and C, which are all in the range [0, 50000], separated by a single space.

N is the cost price of Jame good.
M is the sell price.
P is the total fake money the customer gave Jame.
C is how much Jame paid back to the customer.

Here N < M. And P may be less than M, as customer may pay with some fake money and some true money.

The input is terminated by a line containing 4 zeros.

Output

For one instance, output one line contains exactly one integer, which tells how much Jame lost in the trade. If Jame still earned, just output a negative integer, the absolute value of which tells the money Jame earned.

Sample Input

40 70 100 3040 70 50 2014604 32391 3902 1530 0 0 0

Sample Output

7020-13885

思路：首先顾客给了老板的总金额是：标价+找零（M+C），然后老板给顾客的总价值为：找零+进货价（C+N）按理说老板应该能赚：（标价M+找零C）-（找零C+进货价N）。但是有假钞，所以赚的右变为：（标价M+找零C）-（找零C+进货价N）-假钞（P）

代码

#include <iostream>

using namespace std;

int main()
{
  int N,M,P,C;

  while(cin>>N>>M>>P>>C)
  {   
    if(N==0&&M==0&&P==0&&C==0)
      break;
    cout<<-((M+C)-(N+C)-P)<<endl;
  }
  return 0;
}