Objective

Implement a function that reports whether a single character is alphanumeric: a letter or a decimal digit.

Steps

• Return a non-zero value when c is a letter (a-z or A-Z) or a decimal digit (0-9).
• Return 0 for every other character, including spaces, punctuation, and the zero byte.
• Think of it as the union of two checks: is it a letter, OR is it a digit. Test each range with its own bounds.
• Watch the boundaries: @ sits just before A and [ just after Z in ASCII, so a loose comparison can wrongly accept them.

Objective

Implement a function that reports whether a single character is alphanumeric: a letter or a decimal digit.

Steps

• Return a non-zero value when c is a letter (a-z or A-Z) or a decimal digit (0-9).
• Return 0 for every other character, including spaces, punctuation, and the zero byte.
• Think of it as the union of two checks: is it a letter, OR is it a digit. Test each range with its own bounds.
• Watch the boundaries: @ sits just before A and [ just after Z in ASCII, so a loose comparison can wrongly accept them.