Transcript ULI101

IPC144
Introduction to Programming Using C
Week 1 – Lesson 2
(Pages 5 to 9 in IPC144 Textbook)
Agenda
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Basic Programming Steps (Simple Example):
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Read and understand the question
Develop an algorithm
Code the program in C
Compile the program
Run, Test and Debug the program
C programming Elements:
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main() function
variables and data types
output: printf (output format specifiers)
Programming Steps
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Gather required information (inputs, processing, outputs)
Determine the algorithm – sketch out, in English, how a
human can solve the problem
Write (ie “code”) the program (called the source code)
Compile the source code. Fix any syntax errors and
recompile to create an executable file.
Run executable file with test input(s) and check for
correct output(s). If necessary, debug by finding logical
errors (bugs) and correct source code.
C Programming Basics
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Every C program must contain a function called main()
The name “main” indicates that it is the main part of
the program and is executed first.
main() is followed by the set of braces { and }
which contains the contents of the main function.
C Program Example
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Here is the format of a basic C program:
#include <stdio.h>
main()
{
… statements of C program …
}
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Most C statements end with a ; just as English
sentences end with a period.
C Programming - printf
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A statement used to display formatted output on the
screen is called printf (the “f” indicates that you can
format the the output).
You can use special characters in a printf statement
to format output such as a tab (\t) or newline (\n).
Refer to the IPC144 notes (page 9) for additional
special characters, eg: \” \\
Text that you want to display is surrounded by
parentheses (round brackets) and contained in
double-quotes.
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For example: printf (“Hello!”);
C Programming - printf
Note:
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The printf statement is actually a function that was
created to make it easy for programmers to display
output.
To make certain that you can compile your program
using printf on any computer, you should include a
library that contains standard input and output
function information called stdio.h
This is done by adding a directive at the beginning of
the program before main() as follows:
#include <stdio.h>
Note: No semicolon!
Practice
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From what we have learned so far, let’s try the first
hello.c program
Practice
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How can you actually put your program into the
computer?
You need to connect to Seneca’s matrix computer
First, read “Getting Started” on the IPC144 website
Eg. In MS Windows:
START -> RUN -> telnet matrix.senecac.on.ca
After entering your userid and password a Unix prompt
will be displayed. You then enter Unix commands
Eg: >who
which displays all users currently using matrix
Practice
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First you need to use a text editor to create your
program (referred to as source code).
Use a text editor such as nled, pico, vi, nano, etc… to
enter plain text (no bold, formatting, etc).
Eg: nled hello.c
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All C programming source code files should be saved
with the file extension: lower-case .c
eg
assignment2.c or hello.c
Practice
Compiling a C program:
 The C program must be translated into an executable file, also
known as a binary file, machine-language file, or object file.
 To compile your source code file named hello.c type in the cc
command (to mean compile a C program):
>cc hello.c
 If there are syntax errors then details including as line number
will be displayed
 If there are no syntax errors, then an executable file called a.out
is created
 To run the program enter a.out at the prompt
Eg: >a.out
Practice
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You can also provide a name for the executable file by
using the –o option with the cc command:
eg: cc hello.c –o hello
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The executable file is now contained in the file named
hello, so to run it enter:
hello
and you should see something like this on the screen:
Hello, my name is Fred
Variables
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It would be nice if a computer program could do
something more interesting than display your name!
Variables allow data to be stored in some location in
the computer’s memory.
To have data stored in the computer’s memory, a
storage area must first be created. This is called
declaring a variable. It is important to indicate the
variable’s name and also its data type (eg: integer,
decimal, character, etc…)
Variables
Rules for variable names:
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Only use letters, digits, or underscores
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Cannot begin with a digit
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(eg: customer_age, number1, gstRate, etc…)
(eg, invalid names: 2be, 1stcustomer, 4wheel)
Cannot use keywords such as int, for, if because
they have special meanings
Variables
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Use descriptive names for variables. You can combine multiple
words to form a variable name. You could use underscores to
separate the words but the convention is to use lowercase for
the first word and then capitalize the first letter of each of the
following word(s)
For example:
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customerAge
promptUserGuess
generalSalesTaxRate
Integer Data Type
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First we will study the integer data type in this lesson,
and will study other data types in later lessons.
An integer data type is a whole number that may be
positive or negative. On the matrix computer the
integer data type has a limited range:
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approx. 2109 (
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because the number, including its sign, is stored in 32 bits
-231 to 231-1,
or
-2147483648 to 2147483647)
Variables
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At the beginning of the main() program, you should
first declare your variables and indicate their data
type. int is used to represent an integer data type.
Here is a declaration of two integer variables
int length, width;
Note: same data type
variables can be listed using
commas
Note: the declaration
must end with a
semi-colon ;
Variables
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There are many ways to have a variable “hold data”
in the variable such as assigning a value, or
prompting the user to enter a value, even read data
from a file!
A value can be assigned to a variable by using the
assignment operator which is represented by the
equals sign (however don’t say “equals” when you
see the “=“ sign – say “is assigned” instead!)
eg. int length, width;
length = 3;
width = 5;
Note: The value of a variable can
can also be assigned (“initialized”)
when declaring the variable
eg. int length=3, width=5;
Variables
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The printf statement is used to display values of
variables (also in a specified format).
If you want to display the variable’s value in the
printf statement, you must use a “format specifier”
that represents the variable’s data-type. You use
the format specifier %d for int data-type variables.
For example:
int area = 23;
printf(“Value of area is %d\n”, area);
Format specifier for an
integer data-type where
value of area will be inserted
Variable name(s)
(in order) appear
at end of printf
Practice
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From what we have learned so far, you should be able
to start understanding Program #2, rectangle.c, which
calculates the area and perimeter of a rectangle
Practice!!
 TASK #1
 Attend the lab, and learn how to login to matrix then create, compile,
run, and print out a simple C program.
 TASK #2
 Take the answers for questions #1 and #2 in the Exercise
Handout, create a source-code file, then compile, run and verify your
program! Not due, but for practice!
 TASK #3
 Work on question #3 by yourself to plan, create, compile and run
that program. Remember: Practice is the key to success!!