if, else if and else

if

An if runs a block of code only if its condition is true:

#include <iostream>
using namespace std;

int main() {
    int temperature = 35;
    if (temperature > 30) {
        cout << "It's hot! Drink water.\n";
    }
    cout << "Have a nice day.\n";
    return 0;
}

Output

It's hot! Drink water.
Have a nice day.

• The condition goes inside round brackets ( ).
• The code to run goes inside curly braces { }.
• The last line is outside the braces, so it always runs.

else

else gives a second path for when the condition is false:

#include <iostream>
using namespace std;

int main() {
    int number;
    cin >> number;
    if (number % 2 == 0) {
        cout << number << " is even\n";
    } else {
        cout << number << " is odd\n";
    }
    return 0;
}

Input (what the user types)

7

Output

7 is odd

Think of it like this: if/else is a fork in the road. The program checks the sign and takes exactly one of the two paths.

else if

For more than two choices, chain else if. C++ checks the conditions from top to bottom and runs the first one that is true. The rest are skipped:

#include <iostream>
using namespace std;

int main() {
    int marks;
    cin >> marks;
    if (marks >= 90) {
        cout << "Grade A\n";
    } else if (marks >= 75) {
        cout << "Grade B\n";
    } else if (marks >= 50) {
        cout << "Grade C\n";
    } else {
        cout << "Try again\n";
    }
    return 0;
}

Input (what the user types)

82

Output

Grade B

82 is not ≥ 90, but it is ≥ 75, so it prints Grade B and stops checking.

Common mistake: Don't put a semicolon after the condition: if (x > 5); ends the if right there, and the block below always runs.

Tip: If a block has only one line you may leave out the braces, but beginners should always use them. It avoids nasty bugs.