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CHAPTER 3: Introduction to C Programming

CHAPTER 3: Introduction to C Programming. CSEB113 PRINCIPLES of PROGRAMMING CSEB134 PROGRAMMING I by Badariah Solemon. Topics. Steps for Creating, Compiling and Executing a C program Basic Structure of a C Program Formatting Output Writing Comments Errors and Debugging. Topic 1.

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CHAPTER 3: Introduction to C Programming

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  1. CHAPTER 3: Introduction to C Programming CSEB113 PRINCIPLES of PROGRAMMING CSEB134 PROGRAMMING I by Badariah Solemon BS (May 2012)

  2. Topics • Steps for Creating, Compiling and Executing a C program • Basic Structure of a C Program • Formatting Output • Writing Comments • Errors and Debugging BS (May 2012)

  3. Topic 1 Steps for Creating, Compiling and Executing a C program BS (May 2012)

  4. Major Steps Steps: Prepare Compile Link Execute These steps depend on the computer, the OS, and the C IDE that you will use. BS (May 2012)

  5. Step 1: Prepare • Prepare source code (and data files) • Use a text editor to type your source C program statements. • Assign a name to your source program file (.c) and save the file into disk storage. • (optional) Use the text editor to create a data files. Assign names to the data files (.txt or .dat) and save the file BS (May 2012)

  6. Example: Prepare – Visual Studio BS (May 2012)

  7. 2. Compile • Once your C program is properly written, direct the compiler to do compilation process. • C compiler performs: • Preprocessing • Preprocessor reads the source code and prepares the code for the translator. • Translating • Translator translates the code into machine language. • This creates an object code and stores this object code in another file (i.e. object file) BS (May 2012)

  8. Example: Compile – Visual Studio BS (May 2012)

  9. 3. Link (“Build”) • After compilation is completed, call the linker portion of the C compiler. • As you will see later, a C program is made up of many functions and will call on functions in the C library to perform certain operations. • The linker assembles all the functions called by the source code into final executable program (creates .exe file). BS (May 2012)

  10. Example: Link – Visual Studio BS (May 2012)

  11. 4. Execute • Also known as running the C program. • If a program is successfully executed with no more error, it will produce an output. • Otherwise, you must debug (i.e. locate and fix errors) the program. • This is a compiler dependent task. BS (May 2012)

  12. Example: Execute – Visual Studio BS (May 2012)

  13. Topic 2 Basic Structure of a C Program BS (May 2012)

  14. Basic C Structure: Writing a Simple Program pre-processor directives main function heading { statements } //pre-pocessor directives void main(void) { //declarations //executable statements; } 1 2 3 4 #include <stdio.h> void main(void) { //executable statements printf(“I love programming\n”); printf(“You will love it too once ”); printf(“you know the trick\n”); } Color code: Green – Blue – Red – Black – BS (May 2012)

  15. 1. Preprocessor Directives • A C program line begins with # provides an instruction to the C preprocessor • It is executed before the actual compilation is done. • Two most common directives : • #include • #define • In our example (#include <stdio.h>) identifies the header file for standard input and output needed by the printf(). BS (May 2012)

  16. 2. The main() Function • Every C program has a function main • The word main is a C reserved word or keyword. We MUST NOT use it for declaring any other variable or constant. • 4 common ways of main declaration: • Is compiler-dependent void main(void) { } int main(void) { return 0; } main(void) { } main( ) { } NO semicolon (;) BS (May 2012)

  17. 3. The Braces {} • Identify a segment / body of a program • The start and end of a function • The start and end of the selection or repetition block. • Since the opening brace indicates the start of a segment with the closing brace indicating the end of a segment, there must be just as many opening braces as closing braces (this is a common mistake of beginners) BS (May 2012)

  18. 4. Statements • Specify an action to be taken by the computer as the program executes. • Each statement in C needs to be terminated with semicolon (;) • Two types of statements: • Declaration* • The part of the program that tells the compiler the names of memory cells to store values: variables/constant * Refer chapter 4 for detail • Executable statements • Program lines (excluding comments) that are converted to machine language instructions and executed by the computer. int age, total=0.0; BS (May 2012)

  19. The printf() Function • Is a library or built-in function • Used to send data to the standard output (usually the monitor) to be printed according to specific format. • Syntax: • FormatString is a combination of characters, placeholdersand escape sequence. • Ex: printf(FormatString); Each print a single line to the screen printf(“This is C!”); printf(“C is actually very easy”); printf(“Hope you like it.”); Characters enclosed in “ ” – double quotation marks BS (May 2012)

  20. Basic Rules for Writing a C program • C programs consists of functions and the primary function is the main() function - The main() function body is enclosed in braces { } • To use printf() function, you must include this pre-processor directive: #include <stdio.h> • Each statement (declaration and executable statements) in C needs to be terminated with semicolon (;) • C is a case-sensitive language, so in this chapter: • void VoidVOID • mainMainMAIN • printfPrintfPRINTF  X X  X X X X  BS (May 2012)

  21. Topic 4 Formatting Output BS (May 2012)

  22. Use of Escape Sequence • These statements: • print the two strings on a single line to the screen • Means: • To print the two strings on two lines: • add the \nescape sequence • Means: printf(“Welcome to”); printf(“London!”); Welcome toLondon! Welcome to London! printf(“Welcome to\n”); printf(“London!”); BS (May 2012)

  23. Character Escape Sequence • Are used in the printf()function to format the output. BS (May 2012)

  24. Escape Sequence: \n and \t • New line \n: • Display: • Vertical tab \t: • Display: printf(“How do we jump”); printf(“\n\ntwo lines”); How do we jump two lines printf(“I Love\t\tKuala\t\tLumpur.”); I Love Kuala Lumpur. BS (May 2012)

  25. Ways to Connect a C String Literal To connect a string literal that continues on the next line: • Use a backslash \ • Enclose each unfinished string literal in double quotes • Combination of methods 1 & 2 Equivalent to: printf(“From KL with \ Love.\n”); printf(“From “ “KL “ “with” “ love.\n”); printf(“From “ “KL \ with ” “love.\n”); printf(“From KL with love.\n”); BS (May 2012)

  26. Exercise • Write a program to print to the screen the following menu: • Re-write the above program using only one printf() statement • Review Topic 2 – Formatting Output! • We have learned: • How to write a simple C program • How to continue a line • How to use \t, beep \t, and • carriage return \r • How to print special characters %, \, “ BS (May 2012)

  27. Topic 4 Writing Comments BS (May 2012)

  28. Reasons for Writing Comments • A better programmer write comments in their programs • Comments are notes describing what a particular portion of your program does and how it does it (or anything else that you would like to write) • Usually intended for documentation and clarification purposes • Have no effect on program execution. BS (Feb 2012)

  29. Structure of Comments • Structure: Single line: // to begin comment lines Multi-line: /*any text, number or character*/ • Example: • Incorrect comments: /* This is a comment */ // This is known as comment line /* The comments can span into more than one lines */ printf(“Hello!”);// This comment in on same line of a C statement • printf(“Hello!”);/* This comment in on same line of a C statement */ /* Wrong comment 1: no end asterisks and slash /* Wrong comment 2: no end slash * / *Wrong comment 3: there is a blank between / and * */ X X X BS (Feb 2012)

  30. Location of Comments • Comments can be written: • At the very beginning and end of a C program • On lines separate from the code • On the same line as other C code • In a C statement Example: • /* This comment is at the beginning of a C program & • separated from the code • */ • #include <stdio.h> • voidmain(void) // This comment is on the same line as other C code • { • printf /*This comment is legal & in a C statement */(“Hello”); • printf( /*This comment is legal & in a C statement */“Hello”); • } • /* This comment is at the end of the C program */ BS (May 2012)

  31. How to write valuable comments? • Write comments that can enhance the understandability of your program & are of benefit to you • Make them pleasing to the eye and clear • Often looks much better if comments are on lines separate from the code. So, avoid writing comments on the same line as other C code • Some programmers use a banner at the beginning of their programs • Describes things such as name, identifiers name, author, purpose, and date of the program • Example: • /*************************************************** • ** Name: Apples.c * • ** Purpose: Learning how to write comments in C * • ** Date: Written on 01/04/90 * • ***************************************************/ BS (May 2012)

  32. Test your skill • Write a banner for the program written to answer the exercise in slide 25. Include the following information: • Name of source code file • Purpose • Date written • Author BS (May 2012)

  33. Topic 5 Errors and Debugging BS (May 2012)

  34. Basic Debugging • The process of looking for and correcting errors or mistakes that cause your programs to behave unexpectedly. • 3 types of errors: • Syntax errors • Run-time errors • Logic errors BS (May 2012)

  35. 1. Syntax Error • A violation of the C grammar rules, detected during program translation (compilation). • Effect: statements cannot be translated and program cannot be executed • Ex: #include <stdio.h> ; printf(‘I like programming.”); BS (May 2012)

  36. 2. Run-time Error • An attempt to perform an invalid operation, detected during program execution. • Occurs when the program directs the computer to perform an illegal operation, such as dividing a number by zero. • The computer will stop executing the program, and displays a diagnostic message indicates the line where the error was detected * (depends on IDE – Ms Visual Studio: warning) BS (May 2012)

  37. 3. Logic/Design Error • An error caused by following an incorrect algorithm • Very difficult to detect - it does not cause run-time error and does not display message errors. • The only sign of logic error – incorrect program output • Example: Expected output: This is my output Actual output: This is myoutput • Can be detected by testing the program thoroughly, comparing its output to calculated results • To prevent – carefully desk checking the algorithm and written program before you actually type it BS (May 2012)

  38. Debugging in a Nutshell Compile your source code. Correct syntax errors and run-time errors in the region of the first error detected Program executes? N Y Execute program. Look at your output. If it is not correct, look for logic errors. Make sure your program is fully documented and commented. Output is correct? N Y BS (May 2012)

  39. Test your skill • Find and correct errors in the following program. • #<include stdio.h> • Void main (void); • [ • printf(‘Debugging example:\n’); • printf(“Debug this program \; • and look for syntaz errors and logic errors\n”); • printf(“Do not run this program\n; • printf(“You can do it on you own.”): • ] • /******* This is still a simple C program ****** BS (May 2012)

  40. Summary • C compilers operations – prepare, compile, link, execute • C program structure and elements of C language: • Preprocessor directives, main () function, the {} braces, statements • Using printf()function and formatting output using character escape sequence • Writing comments – reason for writing comments, writing valuable comments, structure and location of comments • Types of programming errors - syntax error, run-time error; logic error, and basic debugging techniques BS (May 2012)

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