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

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

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

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

TK1913-C Programming5 TK1913-C Programming 5 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 What are C reserved words? What are C standard identifiers?

TK1913-C Programming6 TK1913-C Programming 6 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 Examples of reserved word: int, void, double, return Examples of standard identifiers: printf, scanf Identifiers

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

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

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

TK1913-C Programming10 TK1913-C Programming 10 Variable Example: Calculate and display the price of a number of apples if the quantity in kg and price per kg are given. quantityprice_per_kgInput:quantity and price_per_kg priceOutput:price pricequantityprice_per_kgProcess:price = quantity * price_per_kg Example: Calculate and display the price of a number of apples if the quantity in kg and price per kg are given. quantityprice_per_kgInput:quantity and price_per_kg priceOutput:price pricequantityprice_per_kgProcess:price = quantity * price_per_kg

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

TK1913-C Programming12 TK1913-C Programming 12 Example: int number1, number2; number1 = 25; number2 = 23; number1 = number2; … Example: int number1, number2; number1 = 25; number2 = 23; number1 = number2; … Variable - Value Assignment number1 ? number2 ? 2523

TK1913-C Programming13 TK1913-C Programming 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; Valid Example:Invalid Example: int x; int y; x = 12;y = 5.75;

TK1913-C Programming14 TK1913-C Programming 14 Variable - Value Assignment Example: int quantity; float price_per_kg, price; quantity = 5; price_per_kg = 4.50; price = quantity * price_per_kg; … 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 Programming15 TK1913-C Programming 15 Example: int quantity; float price_per_kg, price; quantity = 2; price_per_kg = 4.50; price = quantity * price_per_kg; … Example: int quantity; float price_per_kg, price; quantity = 2; price_per_kg = 4.50; price = quantity * price_per_kg; … Variable - Value Assignment quantity ? price_per_kg ? price ?

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

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

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

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