Node:Local variables, Next:Communication via parameters, Previous:Global variables, Up:Scope

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Local Variables

Local variables, on the other hand, are only visible within local scope. They are "trapped" inside their code blocks.

Just as global scope contains many functions, however, each function can contain many code blocks (defined with curly brackets: {...}). C allows blocks within blocks, even functions within functions, ad infinitum. A local variable is visible within its own block and the ones that block contains, but invisible outside its own block.

int a;

/* Global scope.  Global variable 'a' is visible here,
   but not local variables 'b' or 'c'. */

int main()
{
  int b;

  /* Local scope of 'main'.
     Variables 'a' and 'b' are visible here,
     but not 'c'. */

  {
    int c;

    /* Local scope of {...} block within 'main'.
       Variables 'a', 'b', and 'c' are all visible here. */
  }

  exit (0);
}

Local variables are not visible outside their curly brackets. To use an "existence" rather than a "visibility" metaphor, local variables are created when the opening brace is met, and they are destroyed when the closing brace is met. (Do not take this too literally; they are not created and destroyed in your C source code, but internally to the computer, when you run the program.)