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# ITEC113Algorithms and Programming Techniques - PowerPoint PPT Presentation

ITEC113Algorithms 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

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ITEC113Algorithms and Programming Techniques

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## ITEC113Algorithms 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

• 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 ,

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 :

137–62081024

• 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 534.3223440.3333333 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:

• 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.

### 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