Java do-while循环中无限嵌套的for循环的问题

Question

I am coding a lab for my high school comp. sci. class. The objective of the program is to read data from a file, one integer at a time and print an inverted triangle.

The data is a txt file with: 3 3 7 4 (in the file the data is arranged vertically with 3 at the top, but I can't format that here for some reason)

I then changed the .txt extension to .dat

It should print an inverted triangle with the top row being 3 and each successive row having 1 less asterisk (again, I cant figure out how to format this. I tried and it didnt work). If the int is 3 then the top row is 3, if the int is 7 then the top row is 7 etc.

I am getting stuck in a nested for-loop somehow even though I have my decrement operator that should eventually get the loop to terminate, however it does not. You will see the total weirdness.

public class Triangle2_PR31 
{

    public static void main(String[] args) throws IOException 
    { 
        Scanner triScan = new Scanner(new File("pr31.dat"));//reads file
        int a = triScan.nextInt();
        System.out.println(a);//prints number for verification 
        int b;//instantiate

        do
        {
            //a = triScan.nextInt();
            for(int x = 1; x<=a; x--)//main for-loop
            {
                for(b = a; b>=0; b--)//nested for-loop to print asterisks 
                {
                    System.out.print("*");
                    System.out.println(b);//print to see what happened to b
                }
                System.out.println(b);//print to see if loops gets out here
                a--;//decrease a so loop eventually terminates
                //Doesnt get out here
            }
        }       
        while(triScan.hasNext());
        triScan.close();
    }       
}

When the compiler gets to the SOP(b); line in the nested for-loop, the thing goes all the way into negative 50,000 before I manually terminate the program, I let it go to -200,000 once for fun. I do not understand why it does not simply terminate. I stared at eclipse for 10 minutes trying all sorts of different stuff but I cant figure out what is wrong.

Answer 1

You have this evaluation in the first "for":

for (int x = 1; x <= a; x--)

"X" will always be less than a.

It must be for(int x = 1; x <= a; x++) without the double quotes.

Answer 2

您的主要for循环以与a减少相同的速率减少x，因此x永远不会比引起无限for循环的增长大。