IPC144

Introduction to Programming Using C

Week 1 – Lesson 2

(Pages 5 to 9 in IPC144 Textbook)

Agenda

Basic Programming Steps (Simple Example):

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:

main() function variables and data types output: printf (output format specifiers)

Programming Steps

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

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

Here is the format of a basic C program: #include <stdio.h>

main(){ … statements of C program …

}

Most C statements end with a ; just as English sentences end with a period.

C Programming - printf

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.

For example: printf (“Hello!”);

C Programming - printfNote:

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

From what we have learned so far, let’s try the first hello.c program

Practice

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 commandsEg: >who

which displays all users currently using matrix

Practice

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

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

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

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

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:

Only use letters, digits, or underscores(eg: customer_age, number1, gstRate, etc…)

Cannot begin with a digit(eg, invalid names: 2be, 1stcustomer, 4wheel)

Cannot use keywords such as int, for, if because they have special meanings

Variables

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:

customerAge promptUserGuess generalSalesTaxRate

Integer Data Type

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:

approx. 2109 ( -231 to 231-1, or -2147483648 to 2147483647) because the number, including its sign, is stored in 32 bits

Variables

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 typevariables can be listed using commas

Note: the declarationmust end with asemi-colon ;

Variables

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 cancan also be assigned (“initialized”) when declaring the variableeg. int length=3, width=5;

Variables

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 aninteger data-type wherevalue of area will be inserted

Variable name(s)(in order) appearat end of printf

Practice

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!!