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Homework Help: Help with simplistic C code

  1. Oct 23, 2004 #1
    Hi, I am trying to write a loop that will check a users input to be between a certain numeric range in C. The thing is, I expect the person to enter a number, not a character.

    When the person enters a character, the loop becomes infinite. Thats the problem.
    If you look at example source code below:

    #include <stdlib.h>
    int main()
    int number=0;
    printf("input a number\n");
    scanf("%d", &number);
    while (number <1 || number >5)
    printf("incorrect number!!!!!\nput in new number");
    scanf("%d", &number);

    printf("\n your number is %d",number);
    printf("\n your number is: %d",number);
    return 0;

    it works fine for numbers, but if I enter letter 'a' for example, the loop becomes infinite.

    My question is, how do I go about the code such that a character that is inputted instead of a number prints error to screen and prompts user over again?

    I thought a statement like this while (number <1 || number >5) would do the trick, but it does not.
  2. jcsd
  3. Oct 23, 2004 #2
    check the ascii code of the user input. if it isn't in the range of values assigned to numbers, then print an error message.
  4. Oct 23, 2004 #3
    The problem is with the scanf argument. You should instead allow the user to enter an alphanumeric input and add a few lines to parse it and check if it is indeed a number (and not a spurious input).
  5. Oct 23, 2004 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    You should try to avoid using scanf entirely... in this case you're interested in a single digit, so getchar() would be simple to use.
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