Conditions and Loops

C++ conditions and loops work like most languages, with a few details that matter for correctness.

if Statements

Conditions are numeric or boolean. Be explicit rather than relying on implicit conversions.

int score = 72;

if (score >= 70) {
    std::cout << "A\n";
} else if (score >= 60) {
    std::cout << "B\n";
} else {
    std::cout << "Keep working\n";
}

switch

A switch compares one value against cases. Without break, execution falls through to the next case, which is rarely intended.

switch (grade) {
    case 'A':
        std::cout << "Excellent\n";
        break;
    case 'B':
        std::cout << "Good\n";
        break;
    default:
        std::cout << "Keep going\n";
}

Loops

Use a for loop when the number of iterations is known and a while loop when it depends on a condition.

for (int i = 1; i <= 12; i++) {
    std::cout << "7 x " << i << " = " << 7 * i << "\n";
}

int countdown = 3;
while (countdown > 0) {
    std::cout << countdown << "\n";
    countdown--;
}

Practice

1. Print the grade for a score.
2. Use switch to print a day name from a number.
3. Print all even numbers from 1 to 20.

Hands-on exercise

Print the numbers 1 to 30.
For multiples of 3 print Fizz, for multiples of 5 print Buzz, and for multiples of both print FizzBuzz.

Recap

Conditions choose branches, switch compares one value and loops repeat work. Watch for missing break statements.