题目大意：
A soldier wants to buy w bananas in the shop. He has to pay k dollars for the first banana, 2k dollars for the second one and so on (in other words, he has to pay i·k dollars for the i-th banana).
He has n dollars. How many dollars does he have to borrow from his friend soldier to buy w bananas?
输入：
输入三个数，N,K,W，1<=K,W<=1000,0<=N<=10^9，N是第一个香蕉的费用，K是士兵拥有的money,W是士兵要买的香蕉个数。
输出：
士兵需要向朋友借多少（q）钱才能买到自己想买的香蕉
题目分析：
1、依次算出所有香蕉需要花多少钱sum；
2、用sum跟K比较（两种情况：K大于等于sum不用借，否则要借）
3、q=K-sum；
源代码：
1 #include<iostream> 2 using namespace std; 3 int main() 4 { 5 int k, n, w, sum = 0, q; 6 cin >> k >> n >> w; 7 for (int i = 1; i <= w; i++) 8 sum += i*k; 9 if (n == sum||n>sum) 10 cout << "0" << endl; 11 else 12 { 13 q = sum - n; 14 cout << q << endl; 15 } 16 17 return 0; 18 19 }
心得：题目比较简单，但各种情况要考虑到，写代码时最开始就只想到要借钱的那一部分，没有想到还有不借的。犯的错误比较低级。。。。。继续加油吧！O(∩_∩)O~~~