C语言相关程序

#include<iostream.h>

void main()
{
	float grade[20];
	float sum=0;
	int num;
	int classes=0;
	do
	{
		cout<<"enter grade for classes"<<classes<<":"<<endl;
		cin>>grade[classes];
	}
		while(*(grade+classes++)>0);
			num=classes-1;
		for(classes=0;classes<num;classes++)
		{
			sum+=*(grade+classes);
		}
		cout<<"the average_grade is: "<<sum/num<<endl;
}