If else statements are used to implement a selection structure. Like any other programming language, C++ also uses the if keyword to implement the decision control instruction.

The condition for the if statement is always enclosed within a pair of parentheses. If the condition is true, then the set of statements following the if statement will execute. And if the condition evaluates to false, then the statement will not execute; instead, the program skips that enclosed part of the code.

An expression in if statements is defined using relational operators. The statement written in an if block will execute when the expression following if evaluates to true. But when the if block is followed by an else block, then when the condition written in the if block turns to be false, the set of statements in the else block will execute.

Following is the syntax of if-else statements:

if (condition) {
    statements;
} else {
    statements;
}

One example where we could use the if-else statement is:

#include <iostream>
using namespace std;
 
int main()
{
    int age;
    cout << "Enter a number: ";
    cin >> age;
    if (age >= 50)
    {
        cout << "Input number is greater than 50!" << endl;
    }
    else if (age == 50)
    {
        cout << "Input number is equal to 50!" << endl;
    }
    else
    {
        cout << "Input number is less than 50!" << endl;
    }
}

Input

Enter a number: 51

Output

Input number is greater than 50!

Note: The else if statement checks for a different condition if the conditions checked above it evaluate to false.