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Chapter Ten

Chapter Ten. Developing UNIX Applications In C and C++. Lesson A. C Language Programming. Objectives. Create simple C programs Debug C programs Use the make utility to revise and maintain source files Identify program errors and fix them Create a simple C programming application.

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Chapter Ten

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  1. Chapter Ten Developing UNIX Applications In C and C++

  2. Lesson A C Language Programming

  3. Objectives • Create simple C programs • Debug C programs • Use the make utility to revise and maintain source files • Identify program errors and fix them • Create a simple C programming application

  4. Introducing C Programming • C is the language in which UNIX was developed and refined • C programming may be described as a language that uses relatively short, isolated functions to break down large complex tasks into small and easily resolved subtasks • This function-oriented design allows programmers to create their own program functions to interact with the predefined system functions to create powerful and comprehensive solutions to applications

  5. Creating a C Program • A C program consists of separate bodies of code known as functions • When these functions are put together in a collection, they become a program • Within the program, the functions call each other as needed and work to solve the problem for which the program was originally designed

  6. Creating a C Program

  7. Creating a C Program • The C library consist of functions that perform file, screen, and keyboard operations and when you need to perform one of these operations, you place a function call to it • In terms of program format, every C function must have a name, and every C program must have a function called main • To include comments in a C program, begin the comment line with /* and end the comment with */

  8. Creating a C Program Using the preprocessor #include directive allowed for the output shown here

  9. Creating a C Program

  10. Creating a C Program

  11. Creating a C Program • Characters are represented internally in a single byte of computer memory, and when representing data in a program as a character constant, enclose it in singe quotes • A string is a group of characters, like a name, which are stored in memory in consecutive locations, and when used as constants in a program, must be enclosed in double quotes

  12. Creating a C Program • Identifiers are meaningful names given to variables and functions • Variables must be declared before using them in a program, and declarations begin with a data type followed by one or more variable names • The scope of a variable is the part of the program in which the variable is defined – if this is done in a function, it is an automatic variable and if done outside a function, it is an external or global variable

  13. Creating a C Program

  14. Generating Formatted Outputwith printf The output of a simple C program

  15. if Statements and C Loops • C programs can use if statements to allow the program to make decisions depending on whether a condition is true or false • C provides three looping mechanisms: the for loop, the while loop, and the do-while loop

  16. if Statements and C Loops The C loop generated the output here

  17. Defining Functions • When a function is defined, its name is declared and its statements are written • If a function is to return a value to the code that called it, the data type of the return value must be declared, too • Sometimes it is necessary to pass data to a function and this data is called an argument

  18. Defining Functions This function received an argument and returned a value as a result of processing the argument

  19. Working with Files in C • Files are continuous streams of data and they are typically stored on disk • File pointers point to predefined structures that contain information about the file • Before using a file, it must be opened • The library function for this is fopen • When done with a file, it must be closed • The library function for this is fclose

  20. Working with Files in C • File input and output (I/O) is performed with many functions in C • fgetc performs character input • fputc performs character output • During an input operation, it is essential to test for the end of a file • feof tests for the end-of-file marker

  21. Using the Make Utility toMaintain Program Source Files • Some programs have many files of source code which must be compiled and linked together • Once compiled, the separate object files are linked together into the executable code

  22. Using the Make Utility toMaintain Program Source Files Two files were compiled and linked to form this source code

  23. Using the Make Utility toMaintain Program Source Files • These multimodule source files can become quite difficult to maintain, especially when only a subset of the files are updated and need compiling • This is where the make utility helps in that it tracks what needs to be recompiled by using the time stamp field for each source file • All that is necessary is a control file, called the makefile, which lists the source files and their relationship to each other

  24. Using the Make Utility toMaintain Program Source Files The make utility helped in generating the program seen here

  25. Using the Make Utility toMaintain Program Source Files The make utility helped in creating this multimodule program

  26. Debugging Your Program • There are many opportunities to make errors in your C programs and the compiler will identify errors made • Common errors include: incorrect syntax, missing semicolons, case-sensitive errors • To correct syntax errors, follow these steps: • Write down the line number and a brief description • Edit the source file • Save and recompile the file

  27. Creating a C Program to Accept Input • Use the scanf function to accept input from the keyboard • scanf uses a control string with format specified in a manner similar to printf • scanf can accept multiple inputs, but keep in mind that this usage can lead to difficult and cumbersome code

  28. Creating a C Program to Accept Input

  29. Creating a C Program to Accept Input

  30. Creating a C Program toAccept Input An example of using C to accept keyboard input

  31. Encoding and Decoding Programs Use the make command to help with encoding and decoding

  32. Encoding and Decoding Programs This program requests the name of the file to encode

  33. Encoding and Decoding Programs The file’s contents are encoded, which is what happens when you encrypt a file

  34. Encoding and Decoding Programs Once files are encoded, or encrypted, they can be decoded or decrypted

  35. Lesson B C++ Programming in a UNIX Environment

  36. Objectives • Create a C++ program that displays information on the screen • Create a C++ program to read a text file • Create a C++ program with overload functions • Create a C++ program that creates a new class object

  37. Introducing C++ Programming • C++ is a programming language that builds on C to add object-oriented capabilities • C and C++ are similar in many ways • C++ uses functions, as does C, but with added dimensions such as function overloading, which makes the functions respond to more than one set of criteria and conditions

  38. Introducing C++ Programming • The major differences between C and C++ languages are: • C follows procedural principles, whereas C++ follows object-oriented principles • C++ introduces a new data class called object, which is a collection of data and a set of operands called methods which manipulate the data

  39. Creating a C++ Program Using C++ instead of C to create a program

  40. Creating a C++ Program That Reads a Text File Using C++ instead of C to read text files

  41. How C++ Enhances C Functions Function overloading allows C++ to take C functions farther

  42. Setting Up a Class A class data structure lets you create abstract data types, such as a class for an object called Cube

  43. Chapter Summary • The C language concentrates on how best to create commands and expressions that can be elegantly formed from operators and operands • C programs often consist of separate files called program modules that are compiled separately into object code and linked to other objects that make up the program • The C program structure begins with the execution of instructions located inside a main function that calls other functions that contain more instructions

  44. Chapter Summary • The make utility is used to maintain the application’s source files • The major difference between C and C++ is that C follows procedural principles and C++ primarily follows object-oriented programming • The standard stream library used by C++ is iostream.h • C++ provides two statements for standard input and output: cin and cout respectively

  45. Chapter Summary • C++ offers a way to define a function so that it can handle multiple sets of criteria – this is called overloading • endl skips a line like “\n” does in the C language • You should use a class in C++ when your program performs specific operations on the data

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