实战数组，for循环 if语句 switch语句 制作一个小明的成绩管理系统

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import java.util.Scanner;

public class GradesManagement {

	public static void main(String[] args) {
		int cod=0;
		int projectsNum;
		double gradePlus;
		int  deletePosition=-100;
		int  updatePosition=0;
		Scanner scanner=new Scanner(System.in);		
	while(true)
	{			
		System.out.println("请输入小明的成绩个数");
		projectsNum=scanner.nextInt();
		double allGrades[]=new double[projectsNum];
		System.out.println("请输入小明所有科目成绩");
		
		for(int i=0;i<=projectsNum-1;i++)
		{   allGrades[i]=scanner.nextDouble();
			System.out.println("科目"+(i+1)+"成绩为："+allGrades[i]);
		}
		
	 do
	  {
		System.out.println("请输入操作码："+"n"+"1增加成绩："+
	                           "2删除成绩："+"n"+"3修改成绩："+
	                           "4查询成绩："+"n"+"5退出系统");
		cod=scanner.nextInt();
		switch(cod)
		{ 
		case 1: 
			System.out.println("请输入你要追加的成绩");
			gradePlus=scanner.nextDouble();
			double gradePlusArray[]=new double[++projectsNum];
			for(int addloop=0; addloop<projectsNum-1;addloop++)
			{
				gradePlusArray[addloop]=allGrades[addloop];   //复制数组
			}
			System.out.println("prohectsNum"+projectsNum);
			gradePlusArray[projectsNum-1]=gradePlus;  //将最后一个加入数组	
			allGrades=new double[projectsNum];
			allGrades=gradePlusArray; //长数组赋值短数组，短数组不会变长，为了变长需要从新new一下需要的长度再赋值就ok
			System.out.println("追加成绩成功！此时成绩个数为："+allGrades.length);
			continue;
		case 2: 
			System.out.println("请输入你要删除的成绩位于第几个");
			deletePosition =scanner.nextInt();
			if(deletePosition<0||deletePosition>projectsNum)
			{
		      System.out.println("输入号码有误请重新输入");continue;
		      
			}
			
			else 
			{
				if(allGrades[deletePosition-1]<=0)
		       { 
		    		 System.out.println("成绩已经不存在，请勿重复操作");continue;
		       }else
		       {
				allGrades[deletePosition-1]=-1;
				System.out.println("删除成功！");
		       }
			}
			continue;
		case 3:  
			     System.out.println("请输入需要修改的成绩位置：");
		         updatePosition=scanner.nextInt();
					if((updatePosition<0||updatePosition>projectsNum))
					{
				      System.out.println("输入号码有误请重新输入");continue;}
		         System.out.println("请输入需要修改的成绩"); 
			     allGrades[updatePosition-1]=scanner.nextDouble();
			     System.out.println("修改成功！");
			continue;
		case 4: 
			for(int i=0;i<allGrades.length;i++)
			{
				if(allGrades[i]>0)
             {System.out.println("成绩"+(i+1)+"为:"+allGrades[i]);}
				else{System.out.println("成绩"+(i+1)+"为空");}
			}
			continue;
		case 5: System.out.println("系统已退出，谢谢使用！");System.exit(0);break;
		default :System.out.println("输入有误！请重新输入");continue;
		}
		
		}while(cod!=1||cod!=2||cod!=3||cod!=4||cod!=5);
	  }	

	}
}