PASS Week 11: Pointers

Example Code for Pointers:
This code will swap the values of 'a' and 'b' using a function and pointers.
USE THIS IF YOU NEED AN EXAMPLE FOR POINTER SYNTAX.

void exchange(int*, int*); //Function prototype

int main(void){
	int a = 5;
	int b = 10;
	exchange(&a,&b); //Function call
	return 0;
}

/* Function definition */
void exchange(int* ptrA, int* ptrB)
{
	int c;
	c = *ptrA;
	*ptrA = *ptrB;
	*ptrB = c;
	return;
}













PROBLEM #1: Using Pointers to Doubles

	1) Prompt the user to input two floating point (double) values and store them in two double variables.
	2) Then you will declare two double POINTER variables that point to the variables declared
	   in the previous step.
	3) Create another double variable called "result".
	4) Now add the two inputs together USING THE POINTER VARIABLES. Assign this value to the result variable,
	   and print it to the screen. (The amount of decimal places or zeroes don't matter).

SAMPLE OUTPUT

Enter in two values:
44.5 23.45
44.50 and 23.45 = 67.95











PROBLEM #2: Pass By Reference

In this program you will modify the program from problem 1 by adding a function that will
be given pointers as input. Passing a pointer to a function is known as "Pass By Reference".
Passing a normal variable to a function (like you've been doing thus far) is known as "Pass By Value".

	1) Using the program from problem 1, create a function called “addNbrs( , , )” that takes
	   three double pointers and returns nothing to the caller.
	2) KEEP ALL OF the local declarations for the two input variables and the user prompts,
	   and output in main. REMOVE THE TWO POINTER VARIABLES IN MAIN.
	3) Call the addNbrs() function in main using the addresses of the two input variables and
	   result variable.
	4) Move the expression (the one that added the pointers) into the new function and assign
	   the result using the pointers passed to the function from main.

SAMPLE OUTPUT

Enter in two values:
44.5 22.43
44.50 and 22.43 = 66.93














PROBLEM #3: Calculating the Area and Perimeter of a Square/Rectangle Using Pointers

	1) Create two double variables and prompt the user for input for them. These are
	   the lengths of 2 adjacent sides of your 4 sided polygon.
	2) Then create two double variables for the area and perimeter and set them to 0.
	3) Create and call a SINGLE function that will compute the area AND perimeter of the polygon using pointers.
	4) This function will take two double variables and two double variable addresses
	   as input, and return nothing. (4 variables total as parameters).
	5) Compute the area and perimeter in the function and store them in the two pointer values that
	   were passed to the function
	6) In main, print the area and perimeter.

SAMPLE OUTPUT

Enter in two values:
33.5 44.6
Area = 1494.10 and the perimeter is: 156.20























PROBLEM #4: Calculating Hours and Minutes from Seconds (You guessed it, using pointers)

Honestly trying to explain this problem is hard, and I think seeing the sample output FIRST
is better. Basically, the user enters in seconds, and you convert it into the following format.
Have hours print no higher than 24, minutes no higher than 60, and seconds no higher than 60.

SAMPLE OUTPUT 1:

Enter in the number of seconds to convert:
12001
3 Hours, 20 Minutes, 1 Seconds


SAMPLE OUTPUT 2:

Enter in the number of seconds to convert:
1234
0 Hours, 20 Minutes, 34 Seconds


Here are the steps:

	1) Create a program that prompts the user to enter in a value for number of
	   seconds using a long data type.
	2) Create a function that will take a value representing seconds as input, and will return
	   the number of hours, minutes and seconds contained in that value of seconds.
	3) The three measures should be returned to the calling function by using pointers.
	4) You may assume that the user will not enter more than 24 hours worth of seconds.















PROBLEM #5: Seperating Numbers to the Left and Right of a Decimal Place

Write a program that uses a function that receives a pointer to a floating-point
number and two integer variables and sends back the integer and fraction parts as
integers using pointers up to the hundredth place. In your test driver or main
function prompt for the user to input a floating point number, then call the
function and output the parts from main after the function returns them using
pointers.

Hint use modulus and division.
So if a user enters in 98.65 , the function should return 98 and 65