question5.java

java课程的资料以及实验的代码

class Q5
{
	public static void main(String args[])
	{
		if (args.length==0) System.exit(1);
		String cardNum=args[0];
		if (cardNum.length()!=16) 
		{
			System.out.println("invalid length\n");
			System.exit(1);
		};
		int sum=0;
		int i,r;
		for (i=2;i<=16;i++,i++) sum+=Integer.parseInt(cardNum.substring(i-1,i));
		for (i=1;i<=15;i++,i++)
		{
			r=Integer.parseInt(cardNum.substring(i-1,i));
			r=r*2;
			if (r<10) sum+=r;
			else sum+=r/10+r%10;
		};
		if (sum%10==0) System.out.println("valid card number");
		else System.out.println("invalid card number");
	}
}