1. You are meant to reject any number of command-line arguments other than one (means `argc` should be `2`).

2. To test whether a given character is numeric/alphabetic, you can use the `isdigit`/`isalpha` function (actually implemented as a macro, so mistakes in code might show up in weird ways), like `if (isalpha(argv[1][j]))`. Or, test a range, like `if (argv[1][j] >= '0' && argv[1][j] <= '9')` or `if (argv[1][j] >= 'A' && argv[1][j] <= 'Z' || argv[1][j] >= 'a' && argv[1][j] <= 'z')` (`&&` has precedence over `||` like `*` has over `+`). If you want to negate that last expression without some `!` in front of everything, have fun with De Morgan's laws (it looks worse than it is). And keep in mind that non-alphabetic does not mean numeric or the other way around. Punctuation is neither nor. So test for good or non-good, not specific bad characters.

3. On hitting a "bad" character and printing a usage notice, return with the required exit code, returning will automatically abort any loops you're in, any code left. On hitting a "good" character, there's no immediate action associated. *After* your loop, you would know the whole word is right.