任何人都知道为什么这段代码不断陷入无限循环 [英] anyone know why this code keeps going in an infinite loop

问题描述

import java.util.Scanner;


public class Lab5
{
	
	 public static void main (String[]args)
         {
		Scanner in = new Scanner(System.in);
            System.out.println("How big is the multiplication");
		int choice = in.nextInt();
                while(choice>=1 && choice<=20)
                {
                System.out.print("\nX\t");
            for(int x = 1; x <= choice; x++)
            {   
                    System.out.print(x+"\t"); 
                     System.out.print("\n\t");  
            }
            for( int l=choice; l<=choice; l++)
            {
                System.out.print("-------");
                System.out.println();
            }
                
            for (int j = 1; j <= choice; j++)
{
System.out.print("row"+choice+"|\t");
for (int i = 1; i <= choice; i++)
{
    System.out.print(i * j + "\t");
}

System.out.println();
}
         
            }
                }
         }

推荐答案

int choice = in.nextInt();
while(choice>=1 && choice<=20)
{
    ...

您的循环基于变量choice中返回的值.但是，在循环结束时，您不会获得新值，也没有任何退出循环的方法.更好的方法是:

Your loop is based in the value returned in the variable choice. However, at the end of the loop you do not get a new value or have any way of breaking out of the loop. A better way would be something like:

int choice;
do
{
    System.out.println("How big is the multiplication");
    choice = in.nextInt();
    if (choice < 1 || choice > 20)
        break;  // exit the loop if choice out of range

    // all other code here

} while(choice > 0);

变量"choice"的值在任何地方都不会增加.因此解决方法是增加它.我的解决方案.告诉我我是否正确....

The value of the variable ''choice'' is not getting incremented anywhere. So the fix will be to increment it. My solution for the issue. Tell me if I am correct....

 while(choice>=1 && choice<=20)
                {
                System.out.print("\nX\t");
            for(int x = 1; x <= choice; x++)
            {   
                    System.out.print(x+"\t"); 
                     System.out.print("\n\t");  
            }
            for( int l=choice; l<=choice; l++)
            {
                System.out.print("-------");
                System.out.println();
            }
                
            for (int j = 1; j <= choice; j++)
{
System.out.print("row"+choice+"|\t");
for (int i = 1; i <= choice; i++)
{
    System.out.print(i * j + "\t");
}
 
System.out.println();
}
  choice++; // Added this line of code as fix        
}

我认为您没有完全做到:

I think you did not do fully:

/*---------------------------------------------------------------------------
// AUTHOR:          (Put your name here)
// FILENAME:        Lab5.java
// SPECIFICATION:   This program is for practicing nested loops.
//                    The first task is to print a multiplication table
//                      whose size is specified by the user.
//                    The second (optional, no extra credit, just for fun)
//                      task is to encode a string entered by the user.
//                      The encryption you will use is as follows: in the ith
//                      word, shift every letter up by i (so if the sentence
//                      is "abc abc abc", it becomes "bcd cde def").
// INSTRUCTIONS:    Read the following code skeleton and add your own code
//                  according to the comments.  Ask your TA or your class-
//                  mates for help and/or clarification.  When you see
//                  //--> or ??? that is where you need to add code.
// LAB LETTER:      (Put your Lab Letter here)
//-------------------------------------------------------------------------*/

//  Import required package (Scanner)
//-->

//Declare class (Lab5)
//-->
//-->
    //Declare the main method
    //-->
    //-->
        //Declare some variables: a Scanner (and initialize) and an integer that holds
        //the user's choice of how big the multiplication table is.
        //-->
        //-->

        //For the second task (optional) declare the following:
        //an integer variable to keep track of what word we're currently operating on,
        //a String array that holds each word int he user's sentence separately
        //a String that holds the encrypted text,
        //Give the strings initial values of "" (empty string but not null),
        //and give the first integer variable an initial value of 0
        //-->
        //-->
        //-->

        //make a do while loop that will repeat until the user enters a valid
        //input (an integer from 1 to 20).

        ???
        {

            //Ask the user how large to make the multiplication table
            //-->
            //Read in the user's input
            //-->

            //output the multiplication table if the user's input is within the
            //appropriate range (1-20)
            ???(???)
            {
                //Print out the following string used for formatting the table "\nX\t"
                //use print, not println
                //-->

                //make a for loop that prints each of the numbers from 1 to the user-specified number
                //putting a tab '\t' character in between each number (all on the same line)
                ???(???; ???; ???)
                        //-->

                //Print out the following string used for formatting the table "\n\t"
                //use print, not println
                        //-->

                //make a for loop that prints out the string "--------"  (on the same line)
                //a number of times equal to the user specified size of the multiplication
                //table (more formatting)
                ???(???; ???; ???)
                        //-->

                //Print a blank line
                //-->


                //make a for loop that will range a variable i from 1 to the user-specified
                //size of the multiplication table. At the start of each row (the outer loop),
                //you should print the current row number and the string "|\t" for formatting
                //Inside of that for loop, do the same for
                //a variable j. Each table entry will be i*j and you should print this as well
                //as tab character '\t' after each entry. Also, after each row is done, you
                //should print a blank line.
                ???(???; ???; ???)
                {
                    System.out.print(??? + "|\t");
                    ???(???; ???; ???)
                    {
                        System.out.print(??? + "\t");
                    }
                    //Print a blank line
                    //-->
                }
            }
            //otherwise print out an error telling the user the input is out of range
            ???
            {
                //-->
            }
        }???(???);
        /*

请参阅最后一部分

See this last part

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