It happens before compile, that is the preprocessor. Substitutions are made only for tokens, and do not take place within quoted strings. Local variable vs. global variable Global variable is declared before the main function. Global variables have availability that is visible everywhere in the program.
Local variable is declared within functions.
The programmer needs to assign the value of the local variable. Local variable is only visible within the function it is declared. In the function local variable is declared, local variable takes precedence of global variable. Pointer arguments enable a function to access and change objects in the function that called it. Malloc returns a pointer to space for an object of size size , or NULL if the request cannot be satisfied.