'A' is a single char, one byte holding the value 65 (the ASCII code for capital A). "A" is a string literal, an array of two chars: 'A' followed by a null terminator '\0' marking the end. The compiler treats them with completely different rules: char c = 'A' works, but char c = "A" is a type error because you're trying to fit a pointer-to-array into a single byte. Single quotes for a character, double quotes for text.
Programming Fundamentals · Interview question
Why is 'A' different from "A"?
A strong answer
What a weak answer sounds like
You know the answer. Do you know what gets you dinged?
Pro breaks down the answer most candidates actually give to this question — and the specific reason an interviewer marks it down. It’s the difference between sounding correct and sounding senior, on all 472 questions.
From the lesson
Variables & Data Types
Named boxes that hold a value. Pick a type, declare, assign, and learn why C makes you say what kind of thing each box holds.