The if-else Control Statement in C
----------------------------------

The "if-else" statement in C is similar to the "if-then-else" statement in
C shell programming.

The simplest form of the command is:

	if (expression) statement;

Example usage:

	if (apples == oranges)
	  bananas = 10;

The general form of the command is:

	if (expression)
	  statement1;
	else
	  statement2;

Example usage:

	if (a > 10)
	  printf("it is large\n");
	else
	  printf("it is small\n");

A more complex form of the command is:

	if (expression1)
	  statement1;
	else if (expression2)
	  statement2;
	else if (expression3)
	  statement3;
		:
		:
	else if (expression_n)
	  statement_n;
	else
	  statement_n+1;

Example usage:

	if (a > 10)
	  printf("it is large\n");
	else if (a > 5)
	  printf("it is medium\n");
	else
	  printf("it is small\n");

Note: No "endif" statement is needed.

An even more complex form of the command would be:

	if (expression1)
	{
	  statement1_1;
	  statement1_2;
		:
	  statement1_m;
	}
	else if (expression2)
	{
		:
	}
	else if (expression3)

		:
		:

	else if (expression_n)
	{
	  statementn_1;
	  statementn_2;
		:
	  statementn_m;
	}
	else
	{
	  statement_n+1_1;
	  statement_n+1_2;
		:
	  statement_n+1_m;
	}

Example usage:

	if (number == 5)
	{
	  a = 10;
	  b = 11;
	}
	else if (number > 5)
	{
	  a = 12;
	  b = 11;
	  printf("Hi there!\n");
	}
	else
	  cop = copper + pigroast + fuzz;


Exercises 4.2 -- Problem #2
---------------------------

(Modified to use command line args)

	a)	if money is in the bank for more than 5 years, 
		then the interest rate is 9.5 percent,
		else the rate is 5.4 percent. 

		Use command line args to input the number of years into the
		variable "num_yrs" and output the appropriate interest rate.

		#include <stdio.h>
		#include <stdlib.h>

		main(int argc, char **argv)
		{
		  float num_yrs = atof(argv[1]);

		  if (num_yrs > 5.0)
		    printf("The interest rate is 9.5 percent.\n");
		  else
		    printf("The interest rate is 5.4 percent.\n");
		}

		Sample output is:

		% prog_4.2 1.0
		The interest rate is 5.4 percent.

		% prog_4.2 5.1
		The interest rate is 9.5 percent.

		% prog_4.2 5
		The interest rate is 5.4 percent.

	b)	How many runs should you do to verify that part a) is
		working properly?  2

		What data should you use to test each?
		Test one value greater than 5 and one less than or equal to 5.