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## ITEC113 Algorithms and Programming Techniques

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### ITEC113 Algorithms and Programming Techniques

C programming: Variables, Expressions Part I

Objectives

- To understand what variables are
- initialization/garbage values
- naming conventions
- To learn about the frequently used data types
- To understand the components of
- an assignment Statements
- arithmetic expressions
- To learn about
- frequently used operators,
- operator precedence

VARIABLES

- Variables are basic data objects manipulated in a program.
- Each variable has to be declared before use.
- Each variable has a name and a data type.
- You can give initial value (variable initialization) on variable declaration.

Examples:

int x;

char gender;

float avg;

float sum=0;

char name[10];

int *fp;

VARIABLES

- Variable declaration allocates a cell in the main memory whose size is determined by the data type
- For example for int 4 bytes are used, for double 8 bytes are used
- When the variable is created in the main memory it contains garbage value
- This is due to the existence of 1’s and 0’s in the memory. 1 means high voltage, 0 means low voltage.
- It is a good idea to initialize variables before first usage.
- A variable name is the symbolic representation of the memory location that is allocated on variable declaration

Rules on Variable Names:

- DO NOT use reserved words as variable names

(e.g. if, else, int, float, case, for, …).

- The first character has to be a letter or underscore. It can not be a numeric digit.

The second and the other characters of the name can be any letter, any number, or an underscore “_”.

Examples

Some valid names:

my_name, m113_1, salary, bluemoon, _at

Some invalid names:

my name, my-name , 1stmonth , salary! , guns&roses ,

Tradition on Variable Names:

These are NOTrules but you can increase the quality of your program by using them!

- Select related and meaningful names indicating tasks of the variables.
- Do not use variable names that exceed 8 characters.
- Use small case letters for variable names.
- Upper case letters are mostly used in the names of symbolic constants.

Variable Declaration:

- Variable declaration is used to introduce the system to the variables that the programmer decides to use on the rest of the program.
- On variable declaration,
- variable name,
- data type

are declared.

- Also you can give the initial valueof the variable on its declaration.

Example : intk ;

intm=15;

floatfnumber= 1.75;

charch=’w’ ;

Data Types of the Variables :

- A variable data type specifies:
- The kind of value a variable can store
- The set of operations that can be applied to the variable
- There are 3 main different data types and their derivations for declaration in ANSI–C.

Data Types and Sizes : (Continued)

- Integers(int) :
- Integers are all numeric values that have no fractional or decimal components.
- Integer numbers may be positive or negative.

Examples :

13 7 –6 208 1024

- C compiler allocates 4 bytes (32 bits) to an integer (int) variable.
- An integer variable can store values in the range
- –32,768 through 32,767
- Derived Integers:
- short, long and unsigned are data types derived from int, and used to keep integer values.
- The sizes of long and short is differentiated from int.
- The data type unsigned is used only with positive integers.

Data Types and Sizes : (Continued)

- The sizes of long and short is differentiated from int.
- The data type unsigned is used only with positive integers.

Data Types and Sizes : (Continued)

Real Numbers:

- C compiler uses float and double data types for storing real numbers.
- The float data type requires 4 bytes and has a precision of seven digits
- This means after the decimal point you can have seven digits

Example:

3.14159 534.322344 0.3333333 0.1234567

- The double data type requires 8 bytes and has a precision of fifteen digits

Example :

-3738.78787878783.1415926535897900.123456789123456

Data Types and Sizes : (Continued)

- We can use Scientific Notation to represent real numbers that are very large or very small in value.
- The letters e or E is used to represent times 10 to the power.

Example:

- 1.23 x 10 5is represented in C as 1.23e5or 1.23e+5or 1.23E5
- 1 x 10 -9is represented in C as 1e-9

Data Types and Sizes : (Continued)

Character : ( char )

- Characters constants are usually used enclosed single quotes

Example: ‘A’ , ‘7’,

- Only one byte of memory location is used by a character variable.
- In ASCII code is used to represent uniquely any one of the available 255 characters

Example:

A is represented by decimal 65 or

8-bit binary 0 1 0 0 0 0 0 1

Data Types and Sizes : (Continued)

Categories of characters :

- Alphabetic Letters :
- ( Upper case : ‘A’ , ‘B’, …….. ‘Z’ )
- ( Lower case : ‘a’ , ‘b’, …….. ‘z’ )
- Numeric digits
- ( ‘1’,’2’,’3’,…………,’9’,’0’ )
- Special Characters
- ( blank, ‘+’,’#’,’-‘,’_’,……..)
- Control Characters
- ( ‘\n’ , ‘\t’ , ……. )

Assignment Statements

- The ‘=‘ sign is an assignment operator.
- Assignment statements replace old values of the variables with the new ones
- An assignment statement assigns a value or a computational result to a variable.

Example

cnt= 1; sum = 0;

ch= ‘Y’;

sum = sum + 1; avg = sum / cnt;

stores values 1 and 0 to cnt and sum.

stores character ‘Y’ to ch

stores computational results to sum and avg

Expressions

- Arithmetic Expressions involve arithmetic operators such as *,+,-,/,%:
- Example : a * 5 + b % 4
- Relational Expressions involve relational operators that compare two values such as >,<,== etc:
- Example: a > b
- Logical Expressions involve the logical andandor operators && and || and are used to combine relational expressions:
- Example: ( a > b && c == 7 )

Arithmetic Expressions

In the Assignment Statement:

M = a * 5 + b % 4 ;

- The expression to the right of the assignment operator ( = ) involves an arithmetic operation that combines arithmetic operands with arithmetic operators.
- The most commonly used arithmetic operators are:
- Addition (+) Operator
- Subtraction (-) Operator
- multiplication (*) Operator
- division (/) Operator
- remainder (%) Operator

For real or integer numbers

For integer numbers only

Operator Precedence Rules

- Arithmetic expressions inside parentheses are executed first (left to right).
- Unary operators ( minus signs and plus signs) are executed before multiplications, divisions and remainder operations.
- Additions and subtractions are executed last.

parentheses

-ve and +ve signs

Mult. Div., and mod.

Add and subtract

Operator Precedence Rules:Examples

- ? =3 + 5* 4
- Evaluated as 3 +(5*4) and the result is 23
- ? = 8 / (5 – 2)
- Evaluated as 8 /3 and the result is 2
- ? = 8 + 12 % 5
- Evaluated as 8 +(12%5) and the result is 10
- ? = 6 * 5 / 2 + 2
- Evaluated as ( (6*5)/2)+ 2 and the result is 17
- ? = 9 – 4 + 2 * 6
- Evaluated as 9 – 4 + (2*6) and the result is 17
- ? = 1 + 2 * (3 + 4)
- Evaluated as 1 +(2 * (3+4)) and the result is 15
- ? = 5 * 2 + 9 % 4
- Evaluated as (5*2) + (9 % 4) and the result is 11
- ? = 5 * 2 % ( 7 – 4)
- Evaluated as (5 * 2)%(7 – 4) and the result is 1

That’s it for now!Next Lecture: More on variables, data types and expressions

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