C :

#include<stdio.h>

float switchgoal(int n)
{
	float num=0.0;
	if(n>=90)
		num=4.0;
	else if(n>=85)
		num=3.7;
	else if(n>=82)
		num=3.3;
	else if(n>=78)
		num=3.0;
	else if(n>=75)
		num=2.7;
	else if(n>=72)
		num=2.3;
	else if(n>=68)
		num=2.0;
	else if(n>=64)
		num=1.5;
	else if(n>=60)
		num=1.0;
	return num;
}

int main()
{
	int n;
	int a[10];
	int b[10];
	float c[10];
	float m;
	float sum;
	int k;
	int i,j;
	while(scanf("%d",&n)!=EOF)
	{
		k=0;
		for(i=0;i<n;i++)
			{
				scanf("%d",&a[i]);
				k+=a[i];
		}
		for(i=0;i<n;i++)
		{
			scanf("%d",&b[i]);
			m=switchgoal(b[i]);
			c[i]=m;
		}
		sum=0;
		for(i=0;i<n;i++)
			sum+=a[i]*1.0*c[i];
		printf("%.2f\n",sum/(k*1.0));
	}
	return 0;
}

C++ :

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

int main()
{
        int n, i, xufen;
        int credit[11];
        int score[11];
        double gpai, count;

        while(scanf("%d",&n) != EOF)
        {
                count = 0.00;
                xufen = 0;
                //获取学分
                for(i = 0; i < n; i ++)
                {
                        scanf("%d",credit + i);
                        xufen += credit[i];
                }
                //获取实际得分
                for(i = 0; i < n; i ++)
                {
                        scanf("%d",score + i);
                        if(score[i] <= 100 && score[i] >= 90)
                        {
                                count += 4.0 * credit[i];
                        }else if(score[i] <= 89 && score[i] >= 85)
                        {
                                count += 3.7 * credit[i];
                        }else if(score[i] <= 84 && score[i] >= 82)
                        {
                                count += 3.3 * credit[i];
                        }else if(score[i] <= 81 && score[i] >= 78)
                        {
                                count += 3.0 * credit[i];
                        }else if(score[i] <= 77 && score[i] >= 75)
                        {
                                count += 2.7 * credit[i];
                        }else if(score[i] <= 74 && score[i] >= 72)
                        {
                                count += 2.3 * credit[i];
                        }else if(score[i] <= 71 && score[i] >= 68)
                        {
                                count += 2.0 * credit[i];
                        }else if(score[i] <= 67 && score[i] >= 64)
                        {
                                count += 1.5 * credit[i];
                        }else if(score[i] <= 63 && score[i] >= 60)
                        {
                                count += 1.0 * credit[i];
                        }else
                        {
                                count += 0 * credit[i];
                        }
                }
                
                //求gpa
                printf("%.2lf\n",count / xufen);
        }

        return 0;
}