Section 6: Conditional Statements

Relational Operators

Relational operators compare two values and return a boolean result: true (1) or false (0).

Example Variables: * a = 10 * b = 15

Operator	Symbol	Example Expression	Result (Boolean)	Result (Integer)
Less than	<	a < b	true	1
Less than or equal	<=	a <= b	true	1
Greater than	>	a > b	false	0
Greater than or equal	>=	a >= b	false	0
Equal to	==	a == b	false	0
Not equal to	!=	a != b	true	1

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Logical Operators

Used to combine conditional statements.

Operator Name	Symbol	Description
AND	&&	Returns true if both statements are true.
OR	||	Returns true if one of the statements is true.
NOT	!	Reverses the result; returns false if the result is true.

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Conditional Structures

1. If-Else Condition

Checks a condition; executes the if block if true, otherwise executes the else block.

// Check if age is NOT between 12 and 50
if(age < 12 || age > 50)
{
    cout << "Eligible";
}
else
{
    cout << "Not Eligible";
}

2. If, Else-If, Else

Used to check multiple conditions in sequence. Example: Finding the maximum of three numbers (a, b, c).

if(a > b && a > c)
    cout << a << endl;
else if(b > c)
    cout << b << endl;
else
    cout << c << endl;

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Short Circuit Evaluation

In logical operations (&&, ||), if the result is determined by the first operand, the second operand is not evaluated (skipped).

Case 1: AND (&&) Logic

• Rule: If the first condition is False, the whole expression is False. The second condition is ignored.
• Visual: if ( False && X ) \(\rightarrow\) Result is False (X is not checked).

Example: if ( a > b && a > c ) * If a=3, b=5: a > b is False. * The compiler stops here. a > c is never executed.

Case 2: OR (||) Logic

• Rule: If the first condition is True, the whole expression is True. The second condition is ignored.
• Visual: if ( True || X ) \(\rightarrow\) Result is True (X is not checked).

Example: if ( a > b || a > c ) * If a=5, b=2: a > b is True. * The compiler stops here. a > c is never executed.

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Dynamic Declaration

If a variable is declared inside a specific block (like an if statement), its memory is allocated only for that scope and is deleted once the program exits that block. The scope is limited to that block only.

1. Scope within a block:

if (...)
{
    int m; // 'm' exists only inside these curly braces
}
// 'm' cannot be accessed here; memory is released.

2. Declaration within condition (C++17 feature):

// Initialize 'c', then check the condition
if(int c = a + b; c > 10)
{
    // 'c' is valid here
}

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Switch Case

A control statement that allows a variable to be tested for equality against a list of values (cases).

int x = 2;
switch(x)
{
    case 1: 
        cout << "One";
        break;
    case 2: 
        cout << "Two";
        break;
    case 3: 
        cout << "Three";
        break;
    default: 
        cout << "Invalid number";
}

Important Notes on Switch:

• Fall-thru: If the break keyword is omitted, execution continues ("falls through") to the next case automatically.
• Integral Types Only: The switch expression must result in an integral type data.
  • Allowed: int, char, long, enum.
  • Not Allowed: float, string.