Transcript Functions Continued

Agenda
 Take-up Lab #7 (Functions)
 Additional C Programming Tools:
 Constants vs. Global Variables
 Additional Formatting with printf
 In-Class Exercise (Using Functions)
Global Variables
 A global variable is a variable that applies to all
parts of a program.
 The global variable is declared at the top of the
program before the main function.
 Although global variables may appear to simplify
programming, they can cause errors since other
people using functions may use the same variable
name for other purposes
 Constantly using global variables is not considered
to be good programming practice.
Global Variables
#include <stdio.h>
int NUM = 1;
void function_1(void);
int main (void) {
printf (“NUM = %d\n”, NUM);
function_1();
printf (“NUM = %d\n”, NUM);
}
void function_1(void){
NUM=NUM+5;
}
Global variables are declared before the
main function. If using global variables, it is
recommended to Capitalize them for identification
The variable NUM is applied
through all functions in the program
When the global variable is changed
within a function, it automatically changes
its value anywhere in the program.
WARNING: The use of global variables
is not considered good programming
practice, and you cannot use global variables
for any of your assignments.
Constants
 A constant is a variable that does not have its
value change within the program, but its value
remains constant throughout all of the functions in
a program.
 Make certain that when using constants, that you
select a constant that doesn’t change such as 60
minutes in an hour or pst=25%
 Constants are declared before the main function
using the #define command.
Constants
#include <stdio.h>
#define NUM 4
void function_1(void);
int main (void) {
printf (“NUM = %d\n”, NUM);
function_1();
printf (“NUM = %d\n”, NUM);
return 0;
}
void function_1(void){
int num2 = 2;
num2 = num2 * NUM;
printf (“num2 = %d\n”, num2);
}
Constant are declared before the
main function. If using constants, it is
recommended to Capitalize them for identification
The value of NUM is applied
through all functions in the program
A constant cannot be changed. It can be
used in other equations, but a constant
cannot be changed in any function.
Formatting with printf
 You can specify the width of a field in
which your value will be displayed – this
allows you to better align data.
 A number in immediately after the %
symbol is used to specify the field width.
 A negative field width will left-justify
values. A positive field width will rightjustify values.
Formatting with printf
Examples (Assume num1=34, num2=2.3, num3=2.5)
Command
printf (“Number:%5d\n”, num1);
printf (“Number:%5.1lf\n”, num2);
printf (“Number:%5.1lf\n”, num3);
printf (“Number:%-5dEnd.\n”, num1);
printf (“Number:%-5.1lfEnd.\n”, num2);
printf (“Number:%-5.1lfEnd.\n”, num3);
Note: If you do not select a field with for a
double that is too large, the entire
unformatted value will be displayed
Output (“-” represent space)
Number:---34
Number:--2.3
Number:--2.5
Number:34---End.
Number:2.3--End.
Number:2.5--End.
In Class Exercise #1
Note the following information:
num1 = 45
num2 = 546
num3 = 34567
num4 = 2.34
num5 = 12.345
num6 = 34.5654
Assuming that “-” represents a space, write the
printf command to display the following:
num1 is:--------45
numbers 1 and 2 are:---45—546
numbers 1 and 2 are:45---546. That’s all!
------2.34
----12.345
---34.5654
In Class Exercise #2
Write a program that will prompt the user for the quantity
and price of an item. The program will calculate and then
display an invoice displaying the amount of the sale, taxes
(pst=8%, gst=7%) and invoice total.
Within your program use constants for pst and gst, and use
a function called double Calc_Taxes (double amount)
that will be used to calculate and return total taxes.
Suggested Answer
#include <stdio.h>
#define GST 7.0
#define PST 8.0
double Calc_Taxes (double);
int main (void){
int quantity;
double price, amount, taxes, total_amount;
printf ("\nEnter the quantity of the item: ");
scanf ("%d", &quantity);
printf ("\nEnter the price of the item: ");
scanf ("%lf", &price);
amount = quantity * price;
taxes = Calc_Taxes (amount);
total_amount = amount + taxes;
printf ("\nSales:\t$%.2lf\tTaxes:\t$%.2lf\tTotal:\t$%.2lf\n\n", amount, taxes, total_amount);
return 0;
}
double Calc_Taxes (double amt){
double total_taxes, pst, gst;
pst = amt * (PST / 100);
gst = amt * (GST / 100);
total_taxes = pst + gst;
return total_taxes;
}