Variables and Constants

1. FTSM Variables and Constants Knowledge: Understand the concept of storage location representation as identifiers Skill: Identify and define data types in C programs Computer Science Department

2. Let’s recap… Which one is the preprocessor instruction? Which one is the main function? Introduction Consider the following example: #include <stdio.h> void main() { printf(“Welcome to UKM\n”); } TK1913-C Programming2

3. Preprocessor Instruction Still remember this diagram? Global Declaration Pengisytiharan globl void main (void) { } Pengisytiharan setempat Local Declaration Statement C Program Structure TK1913-C Programming3

4. Identifiers Identifiers are: • Variable • Constant • Function • Others TK1913-C Programming4

5. What are C standard identifiers? What are C reserved words? Identifiers Syntax Rules: • Consist of only letters, digits and underscores • Cannot begin with a digit • Cannot use C reserved words • Try not to use/redefine C standard identifiers TK1913-C Programming5

6. Identifiers • C Reserved Word • A word that has special meaning in C • C Standard Identifier • A word having special meaning but may be redefined (but is not recommended!!) Examples of reserved word: int, void, double, return Examples of standard identifiers: printf, scanf TK1913-C Programming6

7. Variable • A name associated with a memory cell whose value can change • Needs to be declared: variable_type variable_name; Example:int x; int entry_time, charge; TK1913-C Programming7

8. Variable Types of variable: • Character: char • An individual character value – a letter, a digit or a symbol (e.g. ‘A’, ‘4’, ‘*’) • Integer: int • Whole numbers (e.g. +16, 568, -456) • Float: float • A real number which has a decimal point (e.g. 8.00, 3.1416) • High-level Float: double TK1913-C Programming8

9. Variable Variable Declaration: Example 1: char letter; letter is a character-type variable Example 2: float matric; matric is a ??? variable TK1913-C Programming9

10. Variable Example: Calculate and display the price of a number of apples if the quantity in kg and price per kg are given. • Input:quantity and price_per_kg • Output:price • Process:price = quantity * price_per_kg TK1913-C Programming10

11. Why did we declare it as int? Why did we declare them as float? Variable Example: int quantity; float price_per_kg; float price; TK1913-C Programming11

12. number1 number2 ? ? Variable - Value Assignment Example: int number1, number2; number1 = 25; number2 = 23; number1 = number2; … … 25 23 23 TK1913-C Programming12

13. Variable - Value Assignment • Algorithm • variable  expression • Syntax • variable = expression; • Rules • Expression’s type must be the same as variable’s type Valid Example:Invalid Example: int x; int y; x = 12; y = 5.75; TK1913-C Programming13

14. Variable - Value Assignment Example: int quantity; float price_per_kg, price; quantity = 5; price_per_kg = 4.50; price = quantity * price_per_kg; … How does this program work? TK1913-C Programming14

15. quantity ? price_per_kg ? price ? Variable - Value Assignment Example: int quantity; float price_per_kg, price; quantity = 2; price_per_kg = 4.50; price = quantity * price_per_kg; … 2 4.50 9.00 TK1913-C Programming15

16. Variable - Value Assignment Example: int number1, number2; number1 = 25; number2 = 23; number1 = number2; … … How does this program segment work? TK1913-C Programming16

17. Constant • A value that will not change • Consists of: • Float(e.g. 2.3 2.73F 1.2e-5) • Integer (e.g. 3 67 -2) • Character(e.g. ‘z’ ‘3’ ‘$’ ‘\n’) • String (e.g. “UKM” “1” “5a”) TK1913-C Programming17

18. Exercise To practice what you’ve learned, try exercises on page 83 (Latih Diri) from Pengaturcaraan C TK1913-C Programming18

19. What’s next? …INPUT AND OUTPUT on the way … • If you want to excel: • revise chapter 4 • read chapter 5 & 6 for next week… • Otherwise, you may watch tv, sleep etc. as a preparation for next week classes. End of Lecture 4 TK1913-C Programming19