Chapter 2: Overview of C

1. Chapter 2:Overview of C Problem Solving & Program Design in C Sixth Edition By Jeri R. Hanly & Elliot B. Koffman

2. Figure 2.1 C Language Elements in Miles-to-Kilometers Conversion Program

3. Preprocessor and Library • Preprocessor: A system program that modifies a C program before the compilation. • Preprocessor Directive: A C program line that provides an instruction to the preprocessor • Library: A collection of useful functions and symbols that may be accessed by a program. #include <stdio.h>

4. Constant Macro A name that is replaced by a particular constant value before the program is sent to the compiler. #define KMS_PER_MILE 1.609 Each time the compiler sees KMS_PER_MILE, it will replace it by 1.609. For example: kms = KMS_PER_MILE * miles; would read: kms = 1.609 * miles;

5. Commenting • Those are for the users to remember or understand easier. They are ignored by the preprocessor and the compiler. They provide supplementary information. /* This is a comment */ // This is a comment, as well.

6. Identifiers • Reserved Words Words with special meaning in C; e.g. double. They cannot be used for any other purpose. • Identifiers • Standard Still special words but they can be changed by the programmer; e.g. printf • User-Defined Words to name the memory cell; e.g. KMS_PER_MILE Remark: Names are case sensitive. i.e. area and Area would be two different identifiers.

7. Restrictions • Identifiers must consist of only letters, digits and underscores. • Cannot begin with a digit. • Reserved words cannot be used. • Some compilers take the first 31 characters; so the rest is not important. e.g. my book, 16door, double, ali’sbook ….are invalid. Recommendation: Use capital letters in constant macros and give meaningful names.

8. Variables and Data Types • Variable: A name associated with a memory cell whose value can change. • Data Type: A set of values and operations that can be performed on those values. int  for an integer number (-32767 to 32767) double  for a real number char  for an individual character value Example of a variable declaration: double kms;

9. Figure 2.2 Memory(a) Before and (b) After Execution of a Program

10. Assignment Statements = is read as “gets”, “becomes”, “assigns”, “takes the value of”. variable = expression; x = y + z; x = x + 1; Previous value is overwritten by the new value

11. Figure 2.3 Effect of kms = KMS_PER_MILE * miles;

12. Figure 2.4 Effect of sum = sum + item;

13. Figure 2.5 Effect of scanf("%lf", &miles);

14. Input/Output Operations and Functions • Data can be stored in the memory in two ways: • By assignment • By copying data from an input device into a variable. For example: scanf function • An instruction that displays information stored in the memory is an output operation; e.g. to output data to the screen printf function is used.

15. Placeholder • A symbol beginning with % in a format string that indicates where to display the output value.

16. printf() printf(“Your point is %f out of 100 \n”, grd); Printf: Function name grd: Print list i.e. variables or expressions whose values are displayed. Whole in () is the function argument. \n: Terminate the line. %f: placeholder that indicated where to display the output value.

17. scanf() scanf(format string, input list); scanf(“%lf”, &miles) means we will have 30.5 given to “miles” if number entered is 30.5. e.g. scanf(“%c%c%c”, &letter_1, &letter_2, &letter_3); Will take first letter copied to letter_1, second to letter_2 and third one to letter_3 in the entered order.

18. Figure 2.6 Scanning Data Line Bob

19. Figure 2.7 General Form of a C Program

20. Function Body • Two parts: • Declarations Tell the compiler what memory cells are needed in the function • Executable Statements First translated into machine language then executed Punctuation: , ; { }

21. Figure 2.8 Evaluation Tree for area = PI * radius * radius;

22. Figure 2.9 Step-by-Step Expression Evaluation

23. Figure 2.10 Evaluation Tree and Evaluation for v = (p2 - p1) / (t2 - t1);

24. Figure 2.11 Evaluation Tree and Evaluation for z - (a + b / 2) + w * -y

25. Figure 2.12 Supermarket Coin Value Program

26. Figure 2.12 Supermarket Coin Value Program (cont’d)

27. Figure 2.13 Batch Version of Miles-to-Kilometers Conversion Program

28. Figure 2.14 Miles-to-Kilometers Conversion Program with Named Files

29. Figure 2.15 Compiler Listing of a Program with Syntax Errors

30. Figure 2.16 A Program with a Run-Time Error

31. Figure 2.17 Revised Start of main Function for Supermarket Coin Value Program

32. Figure 2.18 A Program That Produces Incorrect Results Due to & Omission