C++: Control Flow

What you will learn

How to write conditionals and loops in C++, and the difference between for, while, and do-while loops.

if / else if / else

int score = 85;

if (score >= 90) {
    std::cout << "A";
} else if (score >= 80) {
    std::cout << "B";
} else {
    std::cout << "F";
}

Note else if is two words (not elif). Curly braces are required for multi-statement blocks.

Loops

for loop

for (int i = 0; i < 5; i++) {
    std::cout << i << " ";  // 0 1 2 3 4
}

while loop

int i = 0;
while (i < 5) {
    std::cout << i++ << " ";
}

do-while loop (always runs at least once)

int i = 0;
do {
    std::cout << i++ << " ";
} while (i < 5);

Range-based for (C++11+)

int numbers[] = {1, 2, 3, 4, 5};
for (int n : numbers) {
    std::cout << n << " ";
}

Common mistakes

• Writing if (x = 5) instead of if (x == 5) — the first assigns 5 to x and always evaluates to true. Compile with warnings (-Wall) to catch this.
• Forgetting the semicolon at the end of do { ... } while (condition);
• Using = inside a loop condition when you meant ==
• Forgetting that arrays and other container indexes are zero-based

Quick check below!