How do you create a simple macro-like substitution in C?

• A. Using #define NAME value
• B. Using const int NAME = value
• C. Using typedef NAME = value
• D. Using #include NAME

Answer: (A)

Define a name with the preprocessor so it stands in for a value during compilation. A line like #define NAME value tells the preprocessor to replace every occurrence of NAME with value before the compiler sees the code. This is textual substitution, not a typed constant, so there’s no variable or type involved.

Using a constant with a typed declaration, such as const int NAME = value, creates a real constant with a type and scope, so it’s handled differently by the compiler and may occupy space or be optimized differently. A typedef is for creating a new type alias, not substituting a value. Including a file with #include brings in external code, not a value substitution.

For simple constants, the macro approach is direct, but remember macros have no type checking and can introduce pitfalls with expressions—use parentheses to guard complex replacements.