Section 5: C++ Basics

Basic Program Structure

A simple C++ program to take user input and display it.

#include <iostream>
#include <string> // Required for string usage

using namespace std;

int main()
{
    string name;

    cout << "Enter your name: ";
    getline(cin, name);

    cout << "Hello " << name;

    return 0;
}

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Data Types

Data types define the type of data a variable can hold.

Classification Hierarchy

graph TD
    DT[Data Types] --> P[Primitive]
    DT --> D[Derived]
    DT --> UD[User Defined]

    P --> INT[Integer]
    P --> FLT[Float]
    P --> V[Void]

    INT --> i[int]
    INT --> c[char]
    INT --> b[bool]

    FLT --> f[float]
    FLT --> d[double]

    D --> arr[Array]
    D --> ptr[Pointer]
    D --> ref[Reference]
    D --> func[Function]

    UD --> str[Structure]
    UD --> uni[Union]
    UD --> cls[Class]
    UD --> en[Enum]

Primitives & Ranges

Note: Sizes (bytes) can vary based on the compiler and system (16-bit vs 32-bit vs 64-bit).

Data Type	Size (Bytes)	Range (Typical)	Format Specifier / Note
int	2 or 4	\(-32,768\) to \(32,767\) (if 2 bytes)	Integer values
float	4	\(1.5 \times 10^{-45}\) to \(3.4 \times 10^{38}\)	Single precision
double	8	\(5.0 \times 10^{-324}\) to \(1.7 \times 10^{308}\)	Double precision
char	1	\(-128\) to \(127\)	Characters
bool	1	true (1) / false (0)	Boolean logic

ASCII Codes

Computers store characters as numbers (ASCII values). * A - Z: \(65 - 90\) * a - z: \(97 - 122\) * 0 - 9: \(48 - 57\)

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Modifiers

Modifiers alter the meaning of the base data type to fit various situations.

• unsigned: Holds only positive values.
  • unsigned int: Range \(0\) to \(65,535\)
  • unsigned char: Range \(0\) to \(255\)
• long: Increases the size/range.
  • long int: 4 or 8 bytes
  • long double: 12 or 16 bytes (extended precision)

Variable Declaration Examples

int x;              // Declaration
int rollno;         // Variable naming convention
char group = 'A';   // Initialization
float price = 29.5f;

// Valid declarations
int x1;
int _x;

// Invalid declarations
// int 1x; (Cannot start with digit)
// int for; (Cannot use keywords)

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Variables

Definition: Variables are the names given to data storage locations in memory.

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Operators

Type	Symbol	Description
Arithmetic	+, -, *, /, %	Basic math and modulus (remainder)
Relational	<, <=, >, >=	Comparison
Logical	&&, ||, !	Logical AND, OR, NOT
Bitwise	&, |, ^, ~, <<, >>	Bit-level manipulation
Inc/Dec	++, --	Increase or decrease value by 1
Assignment	=	Assigns value from right to left

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Operator Precedence

Determines which operator is performed first in an expression.

Expression: \(x = a + b * c - d / e\)

Evaluation Order: 1. * and / have higher precedence than + and -. 2. \(b * c\) happens first. 3. \(d / e\) happens second. 4. Then addition/subtraction happens from Left to Right.

Precedence Table (Simplified):

Priority	Operator	Associativity
1 (High)	( )	Left to Right
2	*, /, %	Left to Right
3	+, -	Left to Right
4 (Low)	=	Right to Left

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Compound Assignment

Shorthand for modifying a variable.

Operator	Example	Equivalent To
+=	sum += a	sum = sum + a
-=	sum -= b	sum = sum - b
*=	prod *= x	prod = prod * x
/=	quot /= y	quot = quot / y
%=	rem %= z	rem = rem % z
&=	bit &= 1	bit = bit & 1

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Increment & Decrement Operators

Used to increase (++) or decrease (--) a variable by 1.

1. Pre-Increment / Pre-Decrement

• Syntax: ++x or --x
• Action: Change the value first, then use it.

int x = 5;
int y = ++x; 
// x becomes 6 first
// then y becomes 6

2. Post-Increment / Post-Decrement

• Syntax: x++ or x--
• Action: Use the value first, then change it.

int x = 5;
int y = x++;
// y is assigned 5 (original value)
// x becomes 6 AFTER the assignment

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Bitwise Operators

Operations performed at the bit level (0 and 1).

Truth Table:

A	B	A & B (AND)	A | B (OR)	A ^ B (XOR)
0	0	0	0	0
0	1	0	1	1
1	0	0	1	1
1	1	1	1	0

Operators: * & (AND) * | (OR) * ^ (XOR) * ~ (NOT / One's Complement) * << (Left Shift) * >> (Right Shift)

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Enum (Enumeration)

If we want to define our own data type consisting of a set of named integer constants, we can use enum.

Example 1: Days of Week

enum day {mon, tue, wed, thu, fri, sat, sun};
// By default: mon=0, tue=1, wed=2, etc.

int main() {
    day d;
    d = mon;
    // ...
}

Example 2: Departments (Custom Values)

// You can assign specific values
enum dept {CS=1, ECE, IT, CIVIL}; 
// CS=1, ECE=2, IT=3, CIVIL=4 (auto-increment)

int main() {
    dept d;
    d = CS;
}

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Typedef

Used to create a new name (alias) for an existing data type. This helps with readability.

Syntax: typedef <existing_type> <new_name>;

Example:

typedef int marks;
typedef int rollno;

int main() {
    // 'marks' is now treated as 'int'
    marks m1, m2, m3; 

    // 'rollno' is now treated as 'int'
    rollno r1, r2;

    return 0;
}