meljun cortes--it102 intro turbo c computing

8/8/2019 MELJUN CORTES--IT102 Intro Turbo C Computing

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CMPE 150: Introduction toComputing

MELJUN CORTES,BSCS,ACS

Introduction


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Fall 2008 CMPE 150 Introduction to Computing 2

Basic info about the course

Aim: To teach basic programming skills Course web site:

http://www.cmpe.boun.edu.tr/courses/cmpe150/fall2008

There is no difference between the sections.

There are some changes in the organization ofthe course.

5 hours of class every week

1 hour lecture and 2 hours PS (lectured by theinstructor)

2 hours lab (taught by an assistant; studentassistants will also help the assistant)


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VERY IMPORTANT NOTICE All announcements are made through the CMPE150 e-mail list. The

list has been constructed using your e-mail addresses in theRegistration system. Make sure that your address in theRegistration system is:your BOUN address,you check it every day,its quota is not exceeded and it is functional.

(We will re-construct the list after the add-drop period is over, sochange it now if your Registration e-mail address is not from BOUN.) Note that Yahoo, GMail, Hotmail, and similar addresses frequently

have problems or the messages may go to the spam folder. It is completely your responsibility to make sure that your account

receives the messages properly. We will send the announcements

via the mailing list and assume you read it the same day. There aremore than 350 students in this course and we do not have anyadditional means to contact you if your e-mail address is notworking.

NO EXCUSES WILL BE ACCEPTED FOR AN ANNOUNCEMENTALREADY MADE THROUGH THE MAILING LIST.


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Basic info about the course

You will have 2 midterms

1 final

3 projectsthroughout the semester.

The projects are NOT mandatory (except

for CMPE students). However, there willbe a question closely related with theproject in every exam.


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Grading

Midterm 1 30% Midterm 2 30%

Final 40%

CMPE students start with -15 points To compensate for this, they have to submit

all of their projects.


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Exams and labs

The exams are in front of the computer. Youwill use our online compiler in the exams.

You will use the same online compiler also in thelabs. THEREFORE, YOU MAY CONCLUDE

THAT YOU WILL NOT DO WELL IN THEEXAMS IF YOU DO NOT ATTEND THELABS.

No attendance taken in class or lab. However, we STRONGLYrecommend that youattend the labs.


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Exams and labs

You will be assigned a username andpassword for the online compiler. In the exams, you will receive an

additional password. It is yourresponsibility to ensure that no one elsesees this password. NO MERCY ABOUTCHEATING.

We do not increase (or even decrease)your letter grades at the end of thesemester. Dont ask for it.


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Course outline1- Introduction, printf, scanf, variables, operators, constants

2- Data types, assignment type conversions, type casting, post/pre-increment, type casting

3- If, nested if, logical operators, switch4- While, for, do-while5- Nested loops, break, continue

6- Functions, scope, macro-substitution7- Pointers, variable parameters (aka. call by reference or pointers asfunction arguments)

8- Arrays, passing arrays to functions, sorting and binary search9- Strings10- Multi-dimensional arrays

11- Structs12- Review

Note that pointers (except for variable parameters) are notincluded) in CMPE150 anymore.


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Lets get started !

We will first learn how a computeroperates.


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A computer system

A computer system is composed of: a monitor, a keyboard, a mouse, and a case (that contains several

controlling components such asprocessor and alike), and also other peripherals like

CD player (might have been includedin the case),

printer,

scanner, modem, etc.

all connected together


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Input and output devices

InputInput

Input

InputInput

OutputOutput

/Output

/Output


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A computer system

Note that everything could be packed in asingle box, but the concepts are thesame.


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A computer system

Everything we had in the previous slide ishardware. i.e., physical components that implement what

is requested by the software.

HARDWARE

OPERATING SYSTEM

(Windows, Linux, MacOS, etc.)

APPLICATIONS

(Eg: Word, Excel, Explorer, MSN, C Compiler,

your own programs, etc.)

SOFTW

AR


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A computer system

In this course, we will learn how todevelop our own software (using Clanguage), but we need to understand how

our programs will be executed by thehardware.


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CPU: Central Processing Unit

In terms of hardware, what is importantfor us is the CPU.

It does all processing and control.

Everything is controlled and executed by theCPU.


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CPU: Central Processing Unit

Control Unit

Registers

Arithmetic &

Logic Unit

R1

R2...

Rm

IR

...


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Central Processing Unit (CPU)

Control Unit

Registers

Arithmetic &

Logic Unit

How are the instructions executed?

instr 2

instr 3

...

instr n

instr 1

Program

Main Memory

R1

R2...

Rm

IR

...


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Statement vs. Instruction

Our source code (in C) is composed ofstatements. Eg: a=b+c/2;

The corresponding machine code is composed ofinstructions. Eg: 1101001010110010 (divide c by 2) 0110100100100101 (add it to b) 1010110110111011 (put the result in a) CPU is capable of executing instructions, not

statements. Statements may be too complex. Compiler implements each statement using severalinstructions.

Eg: The statement "a=b+c/2;" can be implemented astemp1 = c/2a = b + temp1


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Why have input/output?

A program should not always produce thesame output. O/w, you may keep the result and delete the

program after you run it for the first time.

A program should be consistent; i.e., itshould not produce random results.

Therefore, a program should take someinput, process it, and produce someoutput as the result of that input.


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Execution of an instruction Lets see how an instruction like "a=b+2" is executed.

Assume initially a is 4 andb is 6.

Central Processing Unit (CPU)

Control Unit

Registers Arithmetic &

Logic Unit

...

a=b+2

Main Memory

R1

R2...

Rm

IR

...

a 4

b 66

Program

...

a=b+2 2

8


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Welcome to C Programming Language

Now that we have an overall understanding ofthe computer, we can start writing C programs. Remember:

We write our

programs in

"C language"(whichis an English-like

language)

#include int main(){

printf("Hello world!");return 0;

}

We use a compiler

(such as GCC, Visual

C, Borland C, etc.) totranslate our program

from "C language" to

"machine language"

Compile & Link

This is the executable

code in "machine

language."

This is the only thing

the computer can

understand and run

(execute).

1110101011001001010001010100101000010010100101010101000101001000100101001

(source code) (object code)

(machine code

or

executable code)


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Our first C program: Hello World

Every C program has amain() function. It wraps all the statements to

be executed.

We make use of previouslywritten functions. They areprovided by header files. Typically, we include the

standard input/output header

file, named stdio.h. We write all statements

inside themain() function.

#include

int main()

{

printf("Hello world");

return 0;

}


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Need for input Note that the Hello World program has no

input. Therefore, it always produces the same output:

Hello World So, after we run this program once, we know what it

will always produce. Therefore, we dont need theprogram anymore; we can safely delete it. Definitely this is not what we want. (O/w,

nobody will pay us ) We want to write programs that can take input and

produce different results according to the input. (Details of I/O functions will be covered in the

labs.)


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A program that also performs input

#include

int main()

{

int a, b, c;

printf("Enter two numbers: ");

scanf("%d%d", &a, &b);

c=a+b;

printf("Result is %d ", c);return 0;

}

Enter two numbers:

Result is 13

C Program User screen_

__

\n

58_

Read two integers

(decimals) into

variables a and b

Display the value

of variable c after

the text "Result is"


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Variables

Operations (such as addition, subtraction,etc.) operate on operands.

You need some space to store the value

of each operand. A variable provides storage space for avalue.


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Variables

IMPORTANT: The value of a variable cannever be empty. The value is representedvia multiple bits, each of which is either 0or 1. So, the variable always has a value.

When a local variable is defined, its initialvalue is undefined. In other words, it hasan arbitrary value. (For the moment, wewill not use global variables.)

So, make sure that the variable has avalid value before you perform anyoperation based on that value.


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Variables Each variable consists of multiple bits. E.g.:

Thus, every value is actually stored as asequence of bits (1s and 0s) in the computer.

The number of bits is called the size of thevariable. The size of a variable depends on the type of

the variable, the hardware, the operatingsystem, and the compiler used.

So, in your programs NEVER make assumptions aboutthe size of a variable. The size may change due to the factors listed above,

and your program will not work.

0 0 1 0 0 1 1 0 1 0 1 1 0 1 1 1 213+210+29+27+25+24+22+21+20=991115 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0


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Variables#include

int main

{

int a, b, c;

a=10;

b=3;

c=a-b;

a=b+2;

}

a ...

Program

b ...

c ...

10

7

3

5


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Rules for identifier names While defining names for variables (and also functions,

user-defined types, and constants in the future) youshould obey the following rules: The first character of a name must be a letter or underscore

(_). The remaining characters must be letters, digits, or

underscore. Only the first 31 characters are significant. Avoid reserved words such as int, float, char, etc. as identifier

names.

However, it is better to avoid starting identifier nameswith underscore.

Also remember that C language is case-sensitive. It is a very good practice to use meaningful names.


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Rules for identifier names

Valid:a, a1, count, no_of_students, B56, b_56 Invalid:

1a, say, int, $100

Valid but not recommended:_b56, Tuna, FB, GS, BJK,I_dont_remember_what_this_variable_means,a_very_very_long_identifier_name_1,

a_very_very_long_identifier_name_2


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Standard data types

You have to specify the type of a variablewhen you define it.

There are three standard data types:

Integer (i.e., whole numbers) Float (i.e., real or floating-point numbers)

Characters

We will discuss user-defined types laterin the course.


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Integers Syntax:

int variable_list;wherevariable_list is a comma-separated list of variablenames. Each variable name may be followed by an optionalassignment operator and a value for initialization.

Eg: int a, b=10, c;

Integer is a class of variable types. The most basic oneis int. The size may change, but the leftmost bit is used for

the sign. The remaining bits represent the value inbinary.

Though the size of an int variable may vary, it is alwayslimited, i.e., it contains a limited number of bits.Therefore, the maximum and minimum values that canbe represented by an int variable is limited.


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Integers

For example, assume in your system an integerhas 16 bits.

Leftmost bit is used for the sign, so 15 bits areleft for the value. So, you have 215=32,768positive values, ranging from 0 to 32,767.Similarly, you have 32,768 negative values, this

time ranging from -1 to -32,768. If you have 32 bits (4 bytes) for an integer,than the maximum value is 231=2,147,483,647.

0 0 1 0 0 1 1 0 1 0 1 1 0 1 1 1

sign bit value


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Integers

There are variations of int such as longint, short int, unsigned int. For each one of these types, you may ignore

the word "int" and use long, short, andunsigned, respectively.

The sizes of these types are ordered asfollows:

short int int long int


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Floating-point numbers

Syntax:float variable_list;

Float type is used for real numbers.

Note that all integers may berepresented as floating-point numbers,but not vice versa.


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Similar to integers, floats also have theirlimits: maximum and minimum values arelimited as well as the precision.

Lower limit Upper limitThe value you

want to store

Due to loss of precision, what you actually

store might be this, or this


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There are two variations of float:double and long double. They have wider range and higher precision.

The sizes of these types are ordered asfollows:float double long double


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Characters

Syntax:char variable_list;

Character is the only type that has a

fixed size in all implementations: 1 byte. All letters (uppercase and lowercase,

separately), digits, and signs (such as

+,-,!,?,$,,^,#, comma itself, and manyothers) are of type character.


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Characters

Since every value is represented with bits(0s and 1s), we need a mapping for allthese letters, digits, and signs.

This mapping is provided by a table ofcharacters and their correspondinginteger values. The most widely used table for this purpose

is the ASCII table.


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Characters

The ASCII table contains the values for256 values (of which only the first 128are relevant for you). Each row of thetable contains one character. The rownumber is called the ASCII code of thecorresponding character.(The topic of character encoding isbeyond the scope of this course. So, wewill work with the simplified definitionhere.)


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Characters

Never memorize the ASCII codes. Theyare available in all programming books andthe Internet. (Eg: http://www.ascii-code.com)

What is important for us is the followingthree rules: All lowercase letters (a,b,c,...) are consecutive.

All uppercase letters (A,B,C,...) are consecutive.

All digits are consecutive.
http://www.ascii-code.com/http://www.ascii-code.com/


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ASCII table (partial)ASCII code Symbol ASCII code Symbol ASCII code Symbol ASCII code Symbol

... ... 66 B 84 T 107 k32 blank 67 C 85 U 108 l

37 % 68 D 86 V 109 m

42 * 69 E 87 W 110 n

43 + 70 F 88 X 111 o

... ... 71 G 89 Y 112 p

48 0 72 H 90 Z 113 q

49 1 73 I ... ... 114 r

50 2 74 J 97 a 115 s

51 3 75 K 98 b 116 t

52 4 76 L 99 c 117 u

53 5 77 M 100 d 118 v

54 6 78 N 101 e 119 w

55 7 79 O 102 f 120 x

56 8 80 P 103 g 121 y

57 9 81 Q 104 h 122 z

... ... 82 R 105 i ... ...

65 A 83 S 106 j


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Characters

A character variable actually stores theASCII value of the corresponding letter,digit, or sign.

I/O functions (printf(), scanf(), etc.) dothe translation between the image of acharacter displayed on the screen andthe ASCII code that is actually stored inthe memory of the computer.


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Constants Syntax:

#define constant_name constant_value

As the name implies, variables store values that varywhile constants represent fixed values.

Note that there is no storage when you use constants.

Actually, when you compiler your program, the compilerreplaces the constant name with the value you defined. The pre-processor replaces every occurrence ofconstant_name with everything that is to the right ofconstant_name in the definition. Note that there is no semicolon at the end of the definition.

Conventionally, we use names in uppercase forconstants.


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Enumerated type Used to define your own types. Syntax:

enumtype_name {

item_name=constant_int_value, ...

}variable_list;

By default, the value of the first item is 0, andit increases by one for consecutive items.However, you may change the default value byspecifying the constant value explicitly.

Eg: enum boolean {FALSE,TRUE} v1, v2;enum days {SUN,MON,TUE,WED,THU,FRI,SAT};

enum {one=1,five=5,six,seven,ten=10,eleven} num;

Text in green is optional


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Operators

We will cover the most basic operators in class.More operators will be covered in the labs.

Assignment operator (=) Note that this is not the "equals" operator. It should

be pronounced as "becomes." (Equals is anotheroperator.)

The value of the expression on the RHS is assigned(copied) to the LHS.

It has right-to-left associativity.a=b=c=10;

makes all three variables 10.


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Assignment and type conversion

When a variable of a narrower type isassigned to a variable of wider type, noproblem. Eg: int a=10; float f;

f=a;

However, there is loss of information inreverse direction. Eg: float f=10.9;int a;

a=f;


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Operators Arithmetic operators (+,-,*,/,%)

General meanings are obvious. What is important is the following: If one of the

operands is of a wider type, the result is also of thattype. (Its importance will be more obvious soon.)

Eg: Result of int+float is float. Result of float+double isdouble.

In C language, there are two types of division: integerdivision and float division.

If both operands are of integer class, we perform integer

division and the result is obtained by truncating the decimalpart. Eg: 8/3 is 2, not 2.666667.

If one of the operands is of float class, the result is float. Eg: 8.0/3 or 8/3.0 or 8.0/3.0 is 2.666667, not 2.


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Operators

Remainder operator is %. Both operands mustbe of integer class. Eg: 10%6 is 4 (equivalent to 10 mod 6)

+,-,*,/,% have left-to-right associativity.

That means a/b/c is equivalent to(a/b)/c, but not a/(b/c).


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Operators

Logic operators (&&, ||, !) Logic operators take integer class operands. Zero means false.

Anything non-zero means true.

"&&" does a logical-AND operation. (True onlyif both operands are true.)

"||" does a logical-OR operation. (False only

if both operands are false.) "!" does a negation operation. (Converts true

to false, and false to true.)


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Operators If the first operand of the "&&" operator is false,

the second operand is not evaluated at all (since itis obvious that the whole expression is false). Eg: In the expression below, if the values ofb and c

are initially 0 and 1, respectively,

a = b && (c=2)then the second operand is not evaluatedat all, so c keeps its value as 1.

Similarly, if the first operand of the "||"

operator is true, the second operand is notevaluated at all.



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Operators

Bitwise operators (&, |, ^, , ~) Bitwise operators take integer class operands. For the logic operators, the variable represents a

single logical value, true or false.

For the bitwise operators, each bit of the variablerepresents true or false.

&, |, and ^ perform bitwise-AND, -OR, -XOR,respectively.

>perform left- and right-shifts.

"~" takes bitwise ones complement.


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OperatorsOperation Result

5 & 10(0000 0101 &0000 1010)

0(0000 0000)

5 && 10(0000 0101 &&0000 1010)

1(0000 0001)

5 | 10(0000 0101 |0000 1010)

15(0000 1111)

8 ^ 10(0000 0111 ^0000 1010)

13(0000 1101)

7 2(0000 0111 >> 0000 0010)

1 (0000 0001)

~5(~0000 0101)

-6 (in twos complement)(1111 1010)


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Operators

Other assignment operators (+=, -=, *=,/=, %=) Instead of writing a=a+b, you can write a+=b

in short. Similar with -=, *=, /=, and others.

O


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Operators

Pre/Post increment/decrement operators(++, --) The operator ++ increments the value of the

operand by 1.

If the operator comes BEFORE the variable name,the value of the variable is incremented beforebeing used, i.e., the value of the expression is theincremented value. This is pre-increment.

In post-increment, the operator is used after the

variable name, and incrementation is performedafter the value is used, i.e., the value of theexpression is the value of the variable beforeincrementation.

O


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Operators

Eg:a=10; c=10,

b=++a; d=c++;

Both a and c will be come 11, butbwill be 11 while dis 10.

O


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Operators

Comparison operators (==,!=,


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Fall 2008 CMPE 150 Introduction to Computing

Operators

Symbol Usage Meaning== x == y is x equal to y?

!= x != y is x not equal to y?

> x > y is x greater than y?

< x < y is x less than y?

>= x >= y is x greater than or equal to y?


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Operators

We can create complex expressions byjoining several expressions with logicoperators.


Symbol Usage Meaning

&& exp1 && exp2 AND

|| exp1 || exp2 OR

! ! exp NOT

O t


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Operators

While using multiple operators in thesame expression, you should be carefulwith the precedence and associativity ofthe operands.

Eg: The following does NOT check if a isbetween 5 and 10.bool = 5


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Operator precedence table


Operator Associativity

() [] . -> left-to-right

++ -- + - ! ~ (type) * & sizeof right-to-left* / % left-to-right+ - left-to-right

> left-to-right< >= left-to-right

== != left-to-right

& left-to-right^ left-to-right| left-to-right&& left-to-right|| left-to-right?: right-to-left

= += -= *= /= %= &= ^= |= = right-to-left

, left-to-right

O t


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Operators Precedence, associativity, and order of

evaluation: In the table is given in the previous slide,precedence decreases as you go down.

If two operands in an expression have the sameprecedence, you decide according to the associativity

column. There is a common misunderstanding aboutassociativity.

Note that associativity has nothing to do with the orderof evaluation of the operands.

Order of evaluation of operands is not specified in Clanguage.

It is strongly recommended that you read andunderstand Section 2.12 (pp. 52-54) in the bookby Kernighan & Ritchie.


T ti


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Type casting

Also called coersionor type conversion. It does NOT change the type of avariable. It is not possible to change the

type of a variable. What casting does is to convert the typeof a value.

T ti


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Type casting Eg: int a=10, b=3;

float f, g;f=a/b;g=(float)a/b;

The type of a does not change; it is still andinteger. However, in the expression(float)a/b, the value of a, which is 10, isconverted to float value of 10.0, and then it isdivided byb, which is 3. Thus, we perform float

division and g becomes 3.3333... On the other hand, we perform an integerdivision for f, so it becomes 3.

meljun cortes--it102 intro turbo c computing

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