Variables

Declaring Variables with Limited Scope

1. Variable declared in a wider scope

Here, c is declared in the surrounding scope (for example, inside main), so it remains alive until that scope ends.

This is not memory efficient in terms of scope, because c exists longer than needed.

2. Variable declared inside a block

In this approach, c is limited to this block.

Once the block finishes executing:

• c goes out of scope

• its memory is released automatically

This is better because the variable exists only where it is needed.

3. Variable declared inside if (C++17)

This syntax was introduced in C++17.

• c is created only for this if statement

• It behaves exactly like the previous block-based approach

• c is destroyed after the if statement finishes

This is the cleanest and safest way when a variable is only needed for a condition.

4. Using declaration directly as a condition

Here:

• e is declared and initialized inside the if

• The condition is true if e is non-zero

• e is destroyed after the if block

Again, the variable lives only as long as necessary.

If the expression in the if condition evaluates to 0, then if condition will not be executed, because expression has evaluated to false.