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    <p>I wouldn't recommend using regexc for this problem, especially if you're new to C. You should be able to solve it using some of the basic standard library features. You seem to be on the right general track. You are reading in characters and determining what class they fit in. Since you know that a valid input consists of only numbers and the comma character, you can immediately terminate the program if you encounter anything that's not one of those two things. Here are a few tips that might help.</p> <p>If you're reading a character at a time, <code>getchar</code> might prove easier to use than <code>scanf</code>.</p> <p>Also, <code>isdigit</code> is a function. Instead of saying <code>if (c == isdigit)</code>, you want to say <code>if (isdigit(c))</code>.</p> <p>Your function <code>check_dig</code> is defined to return an <code>int</code>, but there is no <code>return</code> statement in the function. The function needs to be modified to return a value, and <code>main</code> needs to do something with this value. A general rule of thumb is that a function returns zero when it completes successfully, or it returns non-zero on an error. In your case, "success" could mean "the character was valid" and "error" could mean "the character was invalid". Making this change should let you eliminate the global variable <code>value</code>. You can also eliminate the global <code>c</code> if you pass the input to <code>check_dig</code> as a parameter (<code>c</code> would become a local variable inside <code>main()</code>).</p> <p>I recommend that you only use the <code>check_dig</code> function to <em>check</em> the digit, and that you remove the part that reads another character. You should make the decision whether or not to skip a character before calling <code>check_dig</code>. That way, you can separate your "read" code, your "skip" code, and your "check" code. This makes your program easier to read and debug.</p>
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    1. POInput validation from redirected stdin in C
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    1. COThanks that helped alot and I understand using the return values etc, except for the return on the main? I've now got seperate functions for check_digit check_comma and skip_char but i'm wondering how I then use the return value of main from this?
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