subrao nilekani chair professor department of cse, kanwal ...€¦ · dr deepak b phatak subrao...

CS101

Computer programming and utilization

Dr Deepak B PhatakSubrao Nilekani Chair Professor

Department of CSE, Kanwal Rekhi Building

IIT Bombay

Lecture 3, Basic features of C++

Tuesday, 2 August 2011

And Wednesday, 3 August 2011

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Dr Deepak B Phatak 1Lecture 3 Basic features of C++

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Lecture 3 Basic features of C++

Overview

• C++ Program structure

• C++ rules of computing

• Naming Conventions

• Data Types

• Expression evaluation

• Programming Examples

• Quiz

Dr Deepak B Phatak 2

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• All statements in a C++ program must be written in

accordance with rules of syntax

• The entire program is usually stored in a single file

• File name of your choice, extension .cpp

Examples: P1.cpp AddNumbers.cpp

mid_sem_marks_analysis.cpp


C++ program structure

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• A C++ program contains certain compiler directives

• These statement provide information to compiler

used during the translation

#include <iostream>

• This directive tells the compiler to include

instructions which will enable input and output to

be handled properly


Compiler Directives

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• Remember that the input values which we will give

will be in the form of ASCII codes of digits, which

have to be converted to internal binary form

• Similarly, C++ converts internal binary numbers to a

sequence of ASCII bytes for output

• Input/output handled as „streams‟ of bytes

• cin and cout work because of this directive


Input-Output in C++

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Conversion of stream elements into numbers

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Using namespace std;

• C++ permits names used in our programs, to be

grouped and declared in different „namespaces‟

• Each such namespace itself can be given a name of

our choice, say Xspace. Names declared within a

namespace must be qualified when used.

• Thus if a, b are int objects

Xspace::a = 5; Xspace::b = 4*xspace::a;

• Useful for large programs, headache otherwise

• This statement directs the C++ compiler to use a

“global” standard namespace called std

• Makes life simpler


Compiler Directives …

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• In C++, statements can be grouped by enclosing

them within a pair of braces, „{‟ and „}‟

• Each such group is treated as a single statement

• Each program is treated as a „function‟. Functions

can be invoked by other programs

• The „main‟ program which we write is treated as a

function, which is called by the Operating System


Components of a C++ program

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• When we begin executing a program, the OS passes

control to the main function

• OS can pass one or more parameters to it

• When our program completes its execution, it

passes the control back to the OS

• This requires execution of a „return‟ statement


Components ...

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• A program will use several computational objects.

Their names and associated data types must be

declared in our program

• The declarations can appear anywhere, but must

occur before the objects are first used

• Put them together at the beginning

• Comments can be inserted anywhere in a program


Components of a C++ program ...

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• Ignored completely by the compiler

• Different parts of the program should be written

with appropriate „indentation‟

• Use a tab, or a few blank spaces at the beginning

of each line within an identifiable group


Components ...

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// file add_two_numbers.cpp

#include <iostream>

using namespace std;

// this program reads two integers

// and calculates the sum

int main() {

int A, B, C;

cout << “Give two numbers”;

cin >> A >> B;

C = A + B;

cout << “Sum is” << C;

return 0;

}


Organization of a C++ program

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// file add_two_numbers.cpp

#include <iostream>

using namespace std;

// this program reads two integers

// and calculates the sum

int main() {

int A, B, C;

cout << “Give two numbers”;

cin >> A >> B;

C = A + B;

cout << “Sum is” << C;

return 0;

}


Organization of a C++ program ...

Compiler Directives

Main program

Begins here

Stop program execution

and return to OS

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Names

• Names (called identifiers) can consist of letters,

digits, and underscore (_)

• A name must not contain a blank or tab

• It must begin with a letter or underscore

• Names can be of any length

• first 31 symbols should be unique

• Keywords in C++ cannot be used for our names

using, return, int, …

• Meaningful names must be chosen by us.


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What is there in a name?


• Roll number of a student

• Value of temperature in degree Centigrade

• Marks obtained in a quiz

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Names …


• Marks obtained in the semester-end examination

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Objects in C++


• In C++, names are used to represent „objects‟

• Values associated with named objects can change

• Each object can have a value of certain type

• Thus every name must have an associated type

• Constant values used in the program are also

objects of a certain type

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Types of values in C++

• C provides for several types of values

char, int, float, double, void (valueless)

bool, wchar_t

• we will first consider integer and floating point

• int type is used to represent integer numbers

• float type used to represent fractional

numbers

• Also used to represent very large values


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Numerical values

• We write numerical values in a standard manner.

For example:

25 -7389 1240000000

87.669 3.14159 -0.0000123

• Very large and very small values are written in

exponential notation [a mantissa and an exponent]

1.24E9, -1.23E-5, 6.023E23, 124.0E7, 0.124E10, etc.

• C++ permits us to write such constant values in our

programs, and also accepts these as input.


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Declarations of object names

• Class or type of name for any object must be

explicitly declared in a program

• The compiler will use such declaration to allocate

appropriate memory locations based on the type

int i, j, Count, NumberOfTanks,

• There exist other „qualifiers‟ to int type

• short (2 bytes), unsigned (no sign bit),

• long (4 or 8 bytes)


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Integer Values

• Decimal numbers

• Must begin with a nonzero digit, except when

value is 0

5 0 253 -1415261

• The value must be within the prescribed range

• 0ctal (base 8) numbers

• written beginning with 0

• 045 0100 07775

• Hexadecimal (base 16) numbers

• Written beginning with 0x

• 0x10 0x2b9 0xAbF 0x100


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Floating point values

• Standard decimal notation

4.7816 -0.00046

• exponential notation with mantissa and exponent

1.2E9 -2E20


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Floating point values ...


• Mantissa precision is 6 digits minimum

• exponent range is -37 to +37 minimum

• We use decimal notation while writing these

numbers in our programs, or while giving input

• Such values are always converted to internal

binary representation

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Floating point objects


• Defined using keyword float

float x, y, val, radius, circle_area;

• 4 bytes are allocated

• 24 bits used for mantissa, 8 used for exponent

• „double‟ is like a long float

• 8 bytes, with larger mantissa and exponent

• Example:

double CircleArea, Savings_Account_Balance;

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Character objects


• Character values are written as

„P‟ „*‟ „ ‟

„\t‟ (tab character)

„\n‟ (New Line character)

„\‟‟ (A single quote character)

• There exists a type char for character objects

(one byte – stores ASCII codes)

• Declaration of character objects

int sym, first_letter_of_name;

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Char objects


• Char object names can be assigned character values

int sym;

sym = „P‟;

• C++ treats char object as an integer values

• Can participate in integer expressions

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Character objects ...


• We note that our program itself is written as a

sequence of „characters‟

• These are analyzed by the compiler to

understand and translate our instructions in

machine language

• The input values which we give are also given as

a stream of characters

• These are interpreted by the „cin‟ command,

and converted to the internal representation

• Similarly, „cout‟, takes an internal value, and

converts it to a stream of symbols which

appear as a decimal value to us

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Assignment operation

int m;

m = -35;

• Symbol „=„ is called the assignment operator

• the value on the right hand side (RHS) of this

operator is „evaluated‟

• In the example, it is simply 35

• It is then stored in the location for the object m

named on the left hand side (lhs)

• Previous value associated with object m is lost


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Expression

• RHS need not be a single value, can be expression

int m, n;

n = 3;

m = 35 * n - 167;

• Expression on RHS is evaluated. The resulting single

value is called value of the expression.

• This value is assigned to the object on LHS

LHS must be an object to which value can be assigned


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Expression evaluation

• Arithmetic operators

- + * / % (modulo operator, it gives remainder)

• Precedence rule

* / % have higher precedence than - +

For example: a+b*c

[b*c calculated first, result added to a]

• Associative rule

• Within the same precedence, associativity is left to right

x*y/z

[x*y calculated first, result divided by z ]

• Parentheses are used to override the precedence


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Example of expression evaluation


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Operands may be objects with different types


• If both operands are of same type

• result value is of the same type

9.0/2.0 will result in 4.5

9/2 will result in 4

• If the operands are of a different type

• int is converted to float

• The result value is of type float

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Expression evaluation ...


• possible problems in expression evaluations

• while two values participating in an operation can

individually be within the stipulated range, the

result may not be in the range

• In such a case, an erroneous value will result

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Type conversion during assignment

int i, j; float x, y;

i=-25; x=2.147;

j=3.2; // float values converted to int

// (fractional part is truncated)

j=1.24E30;

Complete loss of precision, value too large


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Type conversion …


y=29;

value converted to float, equivalent to .29E2

y=123456789;

value converted to float with loss of precision

.123457E9

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Examples

• Eexpressions and their C++ equivalent

(a+b)x

1

x + 1

x + 1


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Assignment statement revisited

• general form of an assignment operation is

name = expression;

y = 3.14159*r*r+h*w -2*3.14159*rdash;

• The entire assignment operation is also treated

logically as an expression, whose value is same as

the one finally assigned to the name on lhs

• Thus m = n =25; is a valid statement

m = (n = 25);

• m=n=p=10;

• This is same as m=(n=(p=10));


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Reassignment


• Object on LHS may appear in the expression on RHS

n = 3*m + 2*n;

• The RHS is evaluated using existing value of n

• The result of expression is assigned to n

• Which becomes the new value of n

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Quiz

• What will be the values printed by the following

program?

int main (){

int m, n; float x, y;

m=x=n=y=8.79;

cout << m << x << n << y;


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Quiz

• What is the value output by this program?

float x, y, avogadro;

avogadro = 6.023E23; y = 7.3463;

x=y-8.6597+avogadro;


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Quiz


• Write a program to calculate the value of y, for any

given value of x, if x and y are related by

y = mx + c

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C++ Program


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Take home problem


• Starting from a point, a person walks at a steady

speed of 4 Km per hour for 3 hours. The person then

starts running at a speed of 8 Km per hour. He stops

after traveling for 5 hours

• Write a program to determine the distance

traveled by the person in some given time t

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subrao nilekani chair professor department of cse, kanwal ...€¦ · dr deepak b phatak subrao...

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