scanf, prevent input letters

This is a discussion on scanf, prevent input letters within the C Programming forums, part of the General Programming Boards category; Hi, how do i prevent them from entering letters when i ask for numbers, using scanf...

  1. #1
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    scanf, prevent input letters

    Hi, how do i prevent them from entering letters when i ask for numbers, using scanf

  2. #2
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    also what does this mean

    printf ("%d", scanf("%d", &var));

    ? Does this return 1 if the variable is filled, and 0 if its null?

    thanks

  3. #3
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    Quote Originally Posted by renderstream
    Hi, how do i prevent them from entering letters when i ask for numbers, using scanf
    You can't.
    Read: http://faq.cprogramming.com/cgi-bin/...&id=1043284385

    >> printf ("%d", scanf("%d", &var));
    Read up on what scanf() returns to understand what gets printed.
    When all else fails, read the instructions.
    If you're posting code, use code tags: [code] /* insert code here */ [/code]

  4. #4
    Rog
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    Quote Originally Posted by renderstream
    Hi, how do i prevent them from entering letters when i ask for numbers, using scanf
    You can't do it with scanf alone. A common way to pre process input is to read stdin using fgets, scan the buffer for the expected characters, then call sscanf to put the input into the proper variables, or let the user know they messed up and ask them to try again.

    It's a lot of work, and there are easier ways... one reason scanf is seldom used.

    -Rog

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