Lecture #5: Functions and Scope

1. Greetings and felicitations
2. Functions
   1. declarations, prototypes (ANSI, K&R)
   2. definitions
   3. pointers to functions
   4. note problems of forward references (default type int, x - sqrt(4))
   5. note parameter passing convention for floats (K&R raises to double, ANSI doesn't unless no or old prototype)
   6. passing arrays
3. Scope
   1. heap (persistent) v. stack (transient)
   2. show example

Scope Example

/*
 * this is a do-nothing program that demonstrates the
 * scope rules of C.
 */
#include <stdio.h>
#include <stdlib.h>

/*
 * forward declarations
 */
void g(int);
void h(void);

/* the top-level definition */
int variable = 1;

/*
 * the main routine
 */
int main(void)
{
	/* scope is function main */
	int variable = 2;

	printf("main(%d):variable = %d\n", __LINE__, 
								variable);

	/* now an inner block */
	{
		/* scope is the rest of this block */
		int variable = 3;

		printf("main(%d):variable = %d\n", __LINE__, 
								variable);

		/* now an even more inner block */
		{
			/* scope is this block */
			extern int variable;

			printf("main(%d):variable = %d\n", 
						__LINE__, variable);
		}
		/* end innermost block */

		printf("main(%d):variable = %d\n", __LINE__, 
								variable);
	}
	/* end inner block -- back to main block */

	printf("main(%d):variable = %d\n", __LINE__, 
								variable);

	/* now let's show how functions interact with scope */
	g(variable);

	/* bye! */
	return(EXIT_SUCCESS);
}

/*
 * now notice "variable" is a parameter
 * so it (effectively) overrides references to the
 * top-level variable)
 */
void g(int variable)
{
	printf("g(%d):variable = %d\n", __LINE__, variable);
	/* now let's call another function */
	h();
}

/*
 * this function has no declarations, so
 * let's see what it prints
 */
void h(void)
{
	printf("h(%d):variable = %d\n", __LINE__, variable);
}