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CPP

By Santosh Tawde

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Chapter 1

C++ Basics

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Learning Objectives

Introduction to C++

Origins, Object-Oriented Programming, Terms

Variables, Expressions, and �Assignment Statements
Console Input/Output
Program Style
Libraries and Namespaces

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Introduction to C++

C++ Origins

Low-level languages

Machine, assembly

High-level languages

C, C++, ADA, COBOL, FORTRAN

Object-Oriented-Programming in C++

C++ Terminology

Programs and functions
Basic Input/Output (I/O) with cin and cout

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Display 1.1 �A Sample C++ Program (1 of 2)

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Display 1.1 �A Sample C++ Program (2 of 2)

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C++ Variables

C++ Identifiers

Keywords/reserved words vs. Identifiers
Case-sensitivity and validity of identifiers
Meaningful names!

Variables

A memory location to store data for a program
Must declare all data before use in program

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Data Types: �Display 1.2 Simple Types (1 of 2)

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Data Types: �Display 1.2 Simple Types (2 of 2)

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Assigning Data

Initializing data in declaration statement

Results "undefined" if you don’t!

int myValue = 0;

Assigning data during execution

Lvalues (left-side) & Rvalues (right-side)

Lvalues must be variables
Rvalues can be any expression
Example:�distance = rate * time;�Lvalue: "distance"�Rvalue: "rate * time"

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Assigning Data: Shorthand Notations

Display, page 14

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Data Assignment Rules

Compatibility of Data Assignments

Type mismatches

General Rule: Cannot place value of one type into variable of another type

intVar = 2.99; // 2 is assigned to intVar!

Only integer part "fits", so that’s all that goes
Called "implicit" or "automatic type conversion"

Literals

2, 5.75, "Z", "Hello World"
Considered "constants": can’t change in program

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Literal Data

Literals

Examples:

2 // Literal constant int
5.75 // Literal constant double
"Z" // Literal constant char
"Hello World" // Literal constant string

Cannot change values during execution
Called "literals" because you "literally typed"�them in your program!

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Escape Sequences

"Extend" character set
Backslash, \ preceding a character

Instructs compiler: a special "escape�character" is coming
Following character treated as�"escape sequence char"
Display 1.3 next slide

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Display 1.3 �Some Escape Sequences (1 of 2)

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Display 1.3 �Some Escape Sequences (2 of 2)

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Constants

Naming your constants

Literal constants are "OK", but provide �little meaning

e.g., seeing 24 in a pgm, tells nothing about�what it represents

Use named constants instead

Meaningful name to represent data�const int NUMBER_OF_STUDENTS = 24;

Called a "declared constant" or "named constant"
Now use it’s name wherever needed in program
Added benefit: changes to value result in one fix

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Arithmetic Operators:�Display 1.4 Named Constant (1 of 2)

Standard Arithmetic Operators

Precedence rules – standard rules

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Arithmetic Operators:�Display 1.4 Named Constant (2 of 2)

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Arithmetic Precision

Precision of Calculations

VERY important consideration!

Expressions in C++ might not evaluate as �you’d "expect"!

"Highest-order operand" determines type�of arithmetic "precision" performed
Common pitfall!

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Arithmetic Precision Examples

Examples:

17 / 5 evaluates to 3 in C++!

Both operands are integers
Integer division is performed!

17.0 / 5 equals 3.4 in C++!

Highest-order operand is "double type"
Double "precision" division is performed!

int intVar1 =1, intVar2=2;�intVar1 / intVar2;

Performs integer division!
Result: 0!

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Individual Arithmetic Precision

Calculations done "one-by-one"

1 / 2 / 3.0 / 4 performs 3 separate divisions.

First🡪 1 / 2 equals 0
Then🡪 0 / 3.0 equals 0.0
Then🡪 0.0 / 4 equals 0.0!

So not necessarily sufficient to change�just "one operand" in a large expression

Must keep in mind all individual calculations�that will be performed during evaluation!

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Type Casting

Casting for Variables

Can add ".0" to literals to force precision�arithmetic, but what about variables?

We can’t use "myInt.0"!

static_cast<double>intVar
Explicitly "casts" or "converts" intVar to �double type

Result of conversion is then used
Example expression:�doubleVar = static_cast<double>intVar1 / intVar2;

Casting forces double-precision division to take place�among two integer variables!

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Type Casting

Two types

Implicit—also called "Automatic"

Done FOR you, automatically�17 / 5.5�This expression causes an "implicit type cast" to�take place, casting the 17 🡪 17.0

Explicit type conversion

Programmer specifies conversion with cast operator�(double)17 / 5.5� Same expression as above, using explicit cast�(double)myInt / myDouble� More typical use; cast operator on variable

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Shorthand Operators

Increment & Decrement Operators

Just short-hand notation
Increment operator, ++�intVar++; is equivalent to�intVar = intVar + 1;
Decrement operator, --�intVar--; is equivalent to�intVar = intVar – 1;

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Shorthand Operators: Two Options

Post-Increment�intVar++

Uses current value of variable, THEN increments it

Pre-Increment�++intVar

Increments variable first, THEN uses new value

"Use" is defined as whatever "context"�variable is currently in
No difference if "alone" in statement:�intVar++; and ++intVar; 🡪 identical result

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Post-Increment in Action

Post-Increment in Expressions:�int n = 2,� valueProduced;�valueProduced = 2 * (n++);�cout << valueProduced << endl;�cout << n << endl;

This code segment produces the output:�4�3
Since post-increment was used

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Pre-Increment in Action

Now using Pre-increment:�int n = 2,� valueProduced;�valueProduced = 2 * (++n);�cout << valueProduced << endl;�cout << n << endl;

This code segment produces the output:�6�3
Because pre-increment was used

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Console Input/Output

I/O objects cin, cout, cerr
Defined in the C++ library called�<iostream>
Must have these lines (called pre-�processor directives) near start of file:

#include <iostream>�using namespace std;
Tells C++ to use appropriate library so we can�use the I/O objects cin, cout, cerr

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Console Output

What can be outputted?

Any data can be outputted to display screen

Variables
Constants
Literals
Expressions (which can include all of above)

cout << numberOfGames << " games played.";�2 values are outputted:� "value" of variable numberOfGames,� literal string " games played."

Cascading: multiple values in one cout

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Separating Lines of Output

New lines in output

Recall: "\n" is escape sequence for the �char "newline"

A second method: object endl
Examples:

cout << "Hello World\n";

Sends string "Hello World" to display, & escape�sequence "\n", skipping to next line

cout << "Hello World" << endl;

Same result as above

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Formatting Output

Formatting numeric values for output

Values may not display as you’d expect!�cout << "The price is $" << price << endl;

If price (declared double) has value 78.5, you�might get:

The price is $78.500000 or:
The price is $78.5

We must explicitly tell C++ how to output numbers in our programs!

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Formatting Numbers

"Magic Formula" to force decimal sizes:�cout.setf(ios::fixed);�cout.setf(ios::showpoint);�cout.precision(2);
These stmts force all future cout’ed values:

To have exactly two digits after the decimal place
Example:�cout << "The price is $" << price << endl;

Now results in the following:�The price is $78.50

Can modify precision "as you go" as well!

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Error Output

Output with cerr

cerr works same as cout
Provides mechanism for distinguishing�between regular output and error output

Re-direct output streams

Most systems allow cout and cerr to be �"redirected" to other devices

e.g., line printer, output file, error console, etc.

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Input Using cin

cin for input, cout for output
Differences:

">>" (extraction operator) points opposite

Think of it as "pointing toward where the data goes"

Object name "cin" used instead of "cout"
No literals allowed for cin

Must input "to a variable"

cin >> num;

Waits on-screen for keyboard entry
Value entered at keyboard is "assigned" to num

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Prompting for Input: cin and cout

Always "prompt" user for input�cout << "Enter number of dragons: ";�cin >> numOfDragons;

Note no "\n" in cout. Prompt "waits" on same�line for keyboard input as follows:

�Enter number of dragons: ____

Underscore above denotes where keyboard entry�is made

Every cin should have cout prompt

Maximizes user-friendly input/output

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Program Style

Bottom-line: Make programs easy to read and modify
Comments, two methods:

// Two slashes indicate entire line is to be ignored
/*Delimiters indicates everything between is ignored*/
Both methods commonly used

Identifier naming

ALL_CAPS for constants
lowerToUpper for variables
Most important: MEANINGFUL NAMES!

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Libraries

C++ Standard Libraries
#include <Library_Name>

Directive to "add" contents of library file to�your program
Called "preprocessor directive"

Executes before compiler, and simply "copies"�library file into your program file

C++ has many libraries

Input/output, math, strings, etc.

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Namespaces

Namespaces defined:

Collection of name definitions

For now: interested in namespace "std"

Has all standard library definitions we need

Examples:�#include <iostream>�using namespace std;

Includes entire standard library of name definitions

#include <iostream>using std::cin; �using std::cout;

Can specify just the objects we want

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Summary 1

C++ is case-sensitive
Use meaningful names

For variables and constants

Variables must be declared before use

Should also be initialized

Use care in numeric manipulation

Precision, parentheses, order of operations

#include C++ libraries as needed

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Summary 2

Object cout

Used for console output

Object cin

Used for console input

Object cerr

Used for error messages

Use comments to aid understanding of�your program

Do not overcomment

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