infintite loop

This is a discussion on infintite loop within the C Programming forums, part of the General Programming Boards category; I have a pice of code Code: do { clrscr(); printf("\n\n\t\t <<< MAIN MENU >>>"); printf("\n\n\t 1. Insert "); printf("\n\n\t ...

  1. #1
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    Question infintite loop

    I have a pice of code

    Code:
    	do
    	{
    		clrscr();
    		printf("\n\n\t\t <<< MAIN MENU >>>");
    		printf("\n\n\t 1. Insert ");
    		printf("\n\n\t 2. Delete ");
    		printf("\n\n\t 0. Exit ");
    		printf("\n\n\t\t Enter your choice  :  ");
    		scanf("%d",&ch);
    		switch(ch)
    		{
    			case 1 : printf("\n Enter data to be inserted : ");
    				scanf("%d",&data);
    				enqueue(&qarr,data);
    				printf("\n\nThe queue is :-\n\n");
    				display(qarr);
    				break;
    
    			case 2 : printf("\n\nBefore Deletion queue is :-\n\n");
    				display(qarr);
    				dequeue(&qarr);
    				printf("\n\nThe new queue is :-\n\n");
    				display(qarr);
    				break;
    
    			case 0 :exit(0);
    
    			default: printf("\n Invalid Choice, try Again !!!");
    		}
    		printf("\n\n\n\n\t\t Press any key to continue...");
    		getch();
    	}
    	while(1);
    if during runtime i input a character into choice instead of an integer the progam goes into infinite loop.

    I know how to rectify the problem. Bt i don't know why the reason due to which the program is going into an infinite loop. Please help

  2. #2
    msh
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    Code:
    char c;
    
    while ((c = getchar()) != EOF && c != '\n');
    This should consume any characters that were not assigned to variables by scanf().

    NB!
    You can get some funky behavior if there are no characters to consume.
    Disclaimer: This post shows my ignorance at the time of its making. I claim ownership of but not responsibility for all errors in it. Reference at your own peril.

  3. #3
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    Thanks, but can you please tll me why is the program going into an infinite loop in the first place?

  4. #4
    msh
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    Ah. Sure. Because you never do anything to break out of the do-while loop, except in case 0 where you exit the program. There's still input in the buffer that scanf() can't assign to ch so you get the default case again and do-while loop runs again. Ad nauseam.
    Last edited by msh; 02-11-2011 at 02:36 AM.
    Disclaimer: This post shows my ignorance at the time of its making. I claim ownership of but not responsibility for all errors in it. Reference at your own peril.

  5. #5
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    Code:
    int c;
    
    while ((c = getchar()) != EOF && c != '\n');
    Question 12.1

  6. #6
    msh
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    Thanks. I keep missing that.
    Disclaimer: This post shows my ignorance at the time of its making. I claim ownership of but not responsibility for all errors in it. Reference at your own peril.

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