浮点数取模

题目链接：http://codeforces.com/contest/404/problem/B

#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <set>
#include <map>
#include <vector>
#include <queue>
#include <algorithm>
#include <iostream>

using namespace std;

double a, d;
int n;

int main()
{
    cin >> a >> d >> n;
    int cnt = 0;
    double len = 0;
    for (int i = 1; i <= n; i++)
    {
        len += d;
        int temp = len / a;
        len = len - temp * a;
        cnt += temp;
        cnt %= 4;
        if (cnt == 0)
        {
            printf("%.10lf %.10lf
", len, 0.0);
        }
        else if (cnt == 1)
        {
            printf("%.10lf %.10lf
", a, len);
        }
        else if (cnt == 2)
        {
            printf("%.10lf %.10lf
", a - len, a);
        }
        else
        {
            printf("%.10lf %.10lf
", 0.0, a - len);
        }
    }
    return 0;
}

 也可以用浮点数取模函数fmod(a,b);

#include <cstdio>
#include <cmath>

using namespace std;

int main()
{
    double a,d,x,y,s=0.0;
    int n;
    scanf("%lf%lf%d",&a,&d,&n);
    for(int i=1; i<=n; i++)
    {
        s+=d;
        s=fmod(s,4*a);
        if(s <= a)x=s,y=0;
        else if(s <=2*a)x=a,y=s-a;
        else if(s <=3*a)x=a-(s-2*a),y=a;
        else x=0,y=a-(s-3*a);
        printf("%lf %lf
",x,y);
    }
    return 0;
}