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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

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itec113 algorithms and programming techniques

ITEC113 Algorithms and Programming Techniques

C programming: Variables, Expressions Part I

objectives
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
  • 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;

variables1
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
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
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:
  • 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
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
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 continued1
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 continued2
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 continued3
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 continued4
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 continued5
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
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
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
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
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
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
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