Variable Scope

• refers to where variables can be referenced

Global Scope

• outside any functions
• can be used by later blocks of code:

    int g;
    
    int
    main(void)
    {
      g = 0;
    }
  

• only one instance of any name can exist at the same level:

    int a;
    int a;
  

  is illegal

Scope Inside Blocks

• blocks inherit all variables from global scope
• may declare variables with the same name to hide (but not replace) global variables
  • if blocks are nested, variables declared in an inner block may hide variables declared in an outer block
• variables declared inside a block have a different scope from global variables, and may even be of a different type:

  int a;
  
  void f(void)
  {
  	float a;	/* different from global `a' */
  	float b;
  
  	a = 0.0;	/* sets `a' declared in this block to 0.0 */
  			/* global `a' is untouched */
  	{
  		int a;	/* new `a' variable */
  
  		a = 2;	/* outer `a' is still set to 0.0 */
  	}
  	b = a;		/* sets `b' to 0.0 */
  }
  
  /* global `a' is untouched by anything done in f() */
  

• This method of hiding variables is a potential source of bugs and some compilers will issue a warning if a variable is found to be hidden