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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
ITEC113 Algorithms and Programming Techniques

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Slide 1

ITEC113 Algorithms and Programming Techniques

C programming: Variables, Expressions Part I

Slide 2

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

Slide 3

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;

Slide 4

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

Slide 5

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 ,

Slide 6

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.

Slide 7

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’ ;

Slide 8

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.

Slide 9

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.

Slide 10

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.

Slide 11

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

Slide 12

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

Slide 13

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

Slide 14

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’ , ……. )

Slide 15

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

Slide 16

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 )

Slide 17

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

Slide 18

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

Slide 19

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

Slide 20

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


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