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A Guide to Unix Using Linux, Fourth Edition 10-1

Chapter 10

Developing UNIX/Linux Applications in C and C++

At a Glance

Instructor’s Manual Table of Contents

• Overview

• Objectives

• Teaching Tips

• Quick Quizzes

A Guide to Unix Using Linux, Fourth Edition 10-2

Lecture Notes

Overview

In Chapter 10, your students learn how to write, compile, and execute basic C programs.

They also learn how to use the make utility. The make utility is a UNIX/Linux

software development tool that controls compilation as you make changes and

Chapter Objectives

• Understand basic elements of C programming

• Debug C programs

• Create, compile, and test C programs

• Use the make utility to revise and maintain source files

• Identify differences between C and C++ programming

Teaching Tips

Introducing C Programming

1. Explain that UNIX was developed and refined in the C language. Stress that since C is

native to UNIX/Linux, it works best as an application development tool. For example,

daemons are written in C.

Besides Kernighan and Ritchie, Ken Thompson, another AT&T Bell Labs

2. Note that C is a compiled language.

Creating a C Program

1. Use Figure 10-1 to describe how to create a C program, starting from the source file and

ending in the executable program. The roles of the preprocessor, compiler, and linker

should be briefly described.

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In some instances, the linker is not a separate tool because the compiler can be

C Keywords

1. Explain that keywords have special meanings and cannot be used as names for variables

or functions.

2. Table 10-1 shows the C language keywords.

Note that Table 10-1 contains standard keywords for ANSI C. GNU C adds

The C Library

2. Introduce the term function call.

3. Note that the linker joins the code of the library function with a program’s object code

Program Format

2. Stress that every C program must have a main() function. Provide an example of C code

that shows a very basic main() function.

Including Comments

1. Use an example to show how to include comments in a C program.

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Using the Preprocessor #include Directive

1. Use the example provided in the book (see Figure 10-2) to explain what a preprocessor

2. Note that the file stdio.h is called a header file.

Specifying Data Types

1. Use Tables 10-2 and 10-3 to describe the data types available in C.

2. Note that a variable’s data type determines upper and lower limits of its range of values.

Stress that the exact limits of ranges vary among compilers and hardware platforms.

Character Constants

1. Explain that characters are represented internally in a single byte of the computer’s

Using Strings

1. When explaining how to use strings in C, the following points are important to mention:

a. A string is a group of characters.

2. Stress that a character array of size n can hold a string that has n – 1 characters. The

extra character holds the null character.

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Including Identifiers

1. Explain that identifiers are names given to variables and functions.

3. Stress that the following rules should be followed when naming identifiers.

a. The first character must be a letter or an underscore.

4. Provide examples of useful and valid identifier names.

Declaring Variables

2. Use an example to show that you can declare multiple variables of the same type on the

same line.

3. Provide an example to show how to initialize variables with values at the time they are

declared.

Understanding the Scope of Variables

2. Use a couple of examples to show what a local or automatic variable is, and what a

global or external variable is. Make sure students understand the difference of scope

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Using Math Operators

1. Use Table 10-4 and a few examples to show how to use math operators in C.

2. Make sure students understand the difference between ++count and count++.

Generating Formatted Output with printf()

1. Describe the syntax of the printf() function.

3. Use examples and Table 10-5 to describe the most common C format specifiers.

The printf function is a powerful and versatile tool for programmers. However,

note that a malicious user may, in some instances, be able to use format

specifiers for printf to launch a format string attack on a computer that can crash

Quick Quiz 1

1. ____________________ are specialized system processes, such as network printing,

that run in the background.

2. The C ____________________ makes modifications to your program, such as

including the contents of other files and creating constant values.

3. The C ____________________ consists of functions that perform file, screen, and

keyboard operations, as well as many other tasks.

4. In C, the ____________________ symbol denotes the beginning of a comment.

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Using the C Compiler

1. Describe the syntax of the gcc program.

Using the if Statement

2. Use a couple of examples to show how to use if and if-else statements in a C program.

Using C Loops

1. Provide examples for each of the three looping mechanisms in C: for, while, and do-

while.

Defining Functions

2. Use the example provided in the book to show how to define and use a function.

3. Describe the role of a function prototype. Explain that the word void before the name of

the function (in its declaration or definition) indicates that the function does not return a

value.

Using Function Arguments

2. Use the example provided in the book to show how to use function arguments in C.

Using Function Return Values

1. Use the example provided in the book to show how to use function return values in C.

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Working with Files in C

1. Provide code examples to explain the following aspects of working with files in C:

a. C file input/output is designed to use file pointers.

Using the make Utility to Maintain Program Source Files

1. Describe the advantages of breaking down the code of a program into smaller modules,

instead of working with one large source code file.

3. Explain how make can be used to solve the problem described above.

5. Describe the syntax of make and use a sample makefile to show how to define basic

make rules.

6. Use Figure 10-3 to show how to make and run a sample program.

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Debugging Your Program

1. Provide examples of typical syntax errors. Show sample compiler output for these

errors. Note that the compiler generally produces more error lines than the number of

2. Describe the steps that can be followed to correct syntax errors within a program, such

as: (1) record the line numbers indicated in compiler output; (2) fix the errors one by

one (starting with the first line number); and (3) save and recompile.

Creating a C Program to Accept Input

1. Describe the syntax of the scanf() function.

3. Provide some examples to show how to use scanf(). Specifically, note that an

Quick Quiz 2

1. The command for the C compiler in Linux operating systems is

____________________.

2. Using the ____________________ loop is best when you know the number of times

that the loop is to perform.

3. A function ____________________ tells the compiler about the function before the

code for the function is fully defined.

4. Make is a utility for maintaining updates to multiple programs in a project; it uses a

control file called a(n) ____________________.

A Guide to Unix Using Linux, Fourth Edition 10–10

Introducing C++ Programming

1. Explain the most important differences between C and C++. Introduce the following

terms: object-oriented programming, class, object, methods, and function overloading.

Creating a Simple C++ Program

1. Use the example provided in the book to show how to create a simple C++ program.

Specifically, note the use of // for comments and cout << to output text. In addition,

explain why the following lines are needed:

a. #include <iostream>

Creating a C++ Program that Reads a Text File

1. Use the example provided in the book to show how to create a C++ program that reads

a text file.

How C++ Enhances C Functions

1. Use the example provided in the book to show how to use C++ code to enhance C

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Quick Quiz 3

1. Function ____________________ allows functions to respond to more than one set of

criteria and conditions.

2. A(n) ___________________ is a collection of data and a set of operations, called

methods, which manipulate the data.

3. C++ uses // to denote a(n) ____________________ line.

4. The ____________________ function is a part of the ifstream class and reports an

invalid condition with the file access.

Class Discussion Topics

1. Do any students in your class have previous object-oriented programming experience?

2. Remind students that like C, Awk supports a printf() function too. Discuss the

Additional Projects

1. What are C macros? Ask your students to do some research on the #define preprocessor

2. What are the differences between C strings (null-terminated arrays of characters) and

C++ strings (instances of the string class)? Tip: A useful resource is

Additional Resources

1. The C Preprocessor:

2. C Variable Types and Declarations:

Key Terms

➢ assembler — The program that is called by a compiler to translate assembly code into

object code.

➢ assembly language — A low-level language that provides maximum access to all the

computer’s devices, both internal and external. Writing an assembly language program

requires a great deal of coding and time.

➢ automatic variable — A variable declared inside a function and local to the function in

which it is declared.

➢ C — A programming language developed in part to overcome the disadvantages of

assembly language programming, which requires a great deal of coding and time. The

result is a high-level set of easy-to-understand instructions. UNIX was originally written

in assembly language but further developed and refined in C, largely due to the efforts

the screen output library function printf().

➢ daemon — A specialized system process that runs in the background. A daemon

accesses UNIX/Linux system code like any other part of the operating system.

➢ decrement operator (—) — A C/C++ arithmetic operator that decreases the value of a

variable by a specified amount.

function before the code for the function is fully defined.

➢ header file — A file containing the information the compiler needs to process standard

input or output statements.

➢ identifiers — The names given to variables and functions.

➢ increment operator (++) — A C/C++ arithmetic operator that increases the value of a

➢ method — A set of operations that manipulate data; a part of the new data class,

objects, used in the C++ programming language.

➢ null character — A single byte whose bits are all set to zero.

➢ object code — The binary instructions translated from program source code by a

compiler.

begins with the # symbol. An example is #include, which tells the preprocessor to

include another file or library in your program.

➢ scope — The part of the program in which a variable is defined and accessible. The

scope can be either inside or outside a function.

➢ source code — The program code that you create using an editor and that either is

A Guide to Unix Using Linux, Fourth Edition 10–14

Technical Notes for Hands-On Projects