Thread: scanf() protection help

  1. #1
    Registered User
    Join Date
    Sep 2007

    scanf() protection help

    Hello all.
    I've been trying to implement a protective measure for my scanf() functions in my program.
    void add_num(void)
    	int a,b,c;
    		printf("Enter an integer to be added to\n");
    	while (scanf("%d", &a) != 1);
    	printf("Enter a second integer to be added to the first\n");
    	while (scanf("%d", &b) != 1);
    	c = (a + b);
    	printf("%d + %d = %d\n", a,b,c);
    The goal is to get the input from the user, and then ask again if scanf doesn't successfully receive input. The problem here is is that when a user give the program bad input, (Like, a character for instance) the while loop just prints the "enter the integer" message on to infinity and doesn't re-evaluate the input.

  2. #2
    Kernel hacker
    Join Date
    Jul 2007
    Farncombe, Surrey, England
    Yes, you need to clear up whatever is in the input buffer (e.g. a letter). There is a FAQ entry for "How do I clear the input buffer" or something close to that title. FAQ's can be found at the top left of the page.

    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  3. #3
    Deathray Engineer MacGyver's Avatar
    Join Date
    Mar 2007
    You still have a '\n' or some other char in the buffer. You probably want to clear the buffer by reading until you hit a '\n' char before you read from scanf().

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