C++ else Keyword

The else keyword in C++ is used to provide an alternate block of code that executes if the condition in the preceding if statement evaluates to false. It is part of the if-else construct, which allows conditional execution of code blocks based on whether a condition is met.

The else block ensures that one of two blocks of code will always execute, making it useful for handling situations where a decision must be made between two mutually exclusive outcomes.

Syntax

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if (condition) {
    // Code to execute if the condition is true
} else {
    // Code to execute if the condition is false
}
condition
A boolean expression evaluated to determine which block of code to execute.
if block
The block of code executed if the condition evaluates to true.
else block
The block of code executed if the condition evaluates to false.

Examples

Example 1: Using if-else for a Simple Condition

In this example, we will go through a basic if-else construct to determine whether a number is positive or negative.

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#include <iostream>
using namespace std;

int main() {
    int number;

    cout << "Enter a number: ";
    cin >> number;

    if (number >= 0) {
        cout << "The number is positive." << endl;
    } else {
        cout << "The number is negative." << endl;
    }

    return 0;
}

Output:

Enter a number: -5
The number is negative.

Explanation:

  1. The user inputs a number.
  2. If the number is greater than or equal to 0, the if block executes, printing “The number is positive.”
  3. If the number is less than 0, the else block executes, printing “The number is negative.”

Example 2: Using if-else with Multiple Conditions

In this example, we will learn how to use an if-else to determine if a number is even or odd.

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#include <iostream>
using namespace std;

int main() {
    int number;

    cout << "Enter a number: ";
    cin >> number;

    if (number % 2 == 0) {
        cout << "The number is even." << endl;
    } else {
        cout << "The number is odd." << endl;
    }

    return 0;
}

Output:

Enter a number: 7
The number is odd.

Explanation:

  1. The user inputs a number.
  2. If the number is divisible by 2 (remainder is 0), the if block executes, printing “The number is even.”
  3. If the number is not divisible by 2, the else block executes, printing “The number is odd.”

Example 3: Nested if-else Statements

In this example, we will learn how to use a nested if-else statement to categorize a number as positive, negative, or zero.

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#include <iostream>
using namespace std;

int main() {
    int number;

    cout << "Enter a number: ";
    cin >> number;

    if (number > 0) {
        cout << "The number is positive." << endl;
    } else if (number < 0) {
        cout << "The number is negative." << endl;
    } else {
        cout << "The number is zero." << endl;
    }

    return 0;
}

Output:

Enter a number: 0
The number is zero.

Explanation:

  1. The user inputs a number.
  2. If the number is greater than 0, the first if block executes.
  3. If the number is less than 0, the else if block executes.
  4. If neither condition is true, the final else block executes, printing “The number is zero.”

Key Points about else Keyword

  1. The else block executes when the condition in the preceding if statement evaluates to false.
  2. It is always paired with an if statement and cannot exist independently.
  3. Nested if-else statements can handle multiple conditions and outcomes.
  4. It helps control the flow of the program by ensuring one of two code blocks executes based on a condition.