In C, a function declaration (also called a function prototype) tells the compiler about a function's name, return type, and parameters — before it's actually defined or used. It’s like a forward declaration that enables you to call functions before they’re defined. ??

? Syntax of Function Declaration

c
return_type (parameter_list);

Example:

c
int add(int a, #include // Function declarationint add(int, () {    int sum = add(5, 3);  // function call    printf("Sum = %d\n", sum);    return 0;}// Function definitionint add(int a, 
Aspect
Declaration
Definition
Purpose
Tells the compiler the function's signature
Provides the actual code
Ends with
Semicolon (;)
Function body {}
Memory used?
? No
? Yes
? Example Without Declaration (Leads to Error)
c
#include int main() {    int result = multiply(2, 3);  // ? Error if multiply isn't declared    return 0;}int multiply(int a, int b) {    return a * b;}
? Fix: Add int multiply(int, int); before main().