Controlling Program Flow

if (condition) {
    // runs when condition is true
} else if (otherCondition) {
    // runs when otherCondition is true
} else {
    // runs when none of the above are true
}

Evaluates the condition before each iteration. If the condition is false from the start, the body never runs.

int i = 0;
while (i < 10) {
    // ...
    ++i;
}

The key difference from a regular while: the condition is evaluated after the body, so the body is guaranteed to run at least once.

do {
    // ...
} while (expression);

The classic for loop has three optional sections: init, condition, and end expression.

for (int i = 0; i < count; ++i) {
    // ...
}

All Three Sections Are Optional

Any or all of the three sections can be omitted. An empty for loop runs forever:

for (;;) {  // infinite loop — equivalent to while(true)
    // ...
}

Multiple Variables in Init

You can declare multiple variables in the init section, but they must be the same type:

for (int i = 0, j = 10; i < j; ++i, --j) {
    // i goes up, j goes down
}

Multiple Expressions in Condition / End

The exit condition and end expression can reference variables from outside the loop, and the end expression can use the comma operator to update multiple variables:

int extra = 5;
for (int i = 0; i < count && extra > 0; ++i, --extra) {
    // ...
}

Iterates over every element in a range (array, vector, string, etc.) without needing an index:

int nums[] = {1, 2, 3, 4, 5};

for (int n : nums) {
    std::cout << n << "\n";
}

continue

Skips the rest of the current iteration and jumps back to the top of the loop to re-evaluate the condition.

• For for loops, the end expression (++i) is also evaluated before re-checking the condition

for (int i = 0; i < 10; ++i) {
    if (i % 2 == 0) continue;  // skip even numbers
    std::cout << i;              // prints 1 3 5 7 9
}

break

Immediately exits the entire loop block. Execution resumes at the statement after the closing brace.

for (int i = 0; i < 100; ++i) {
    if (i == 5) break;  // exits when i reaches 5
    std::cout << i;
}

Checks the result of an expression against a set of constant values. More readable than a long chain of if/else if when matching a single variable to many possible values.

switch (expression) {
    case CONSTANT_A:
        // ...
        break;
    case CONSTANT_B:
        // ...
        break;
    default:            // optional — runs if no case matched
        // ...
        break;
}

Fallthrough

Without a break, execution falls through into the next case and continues evaluating — it does not stop until it hits a break or the end of the switch. This is usually a bug, but can be intentional.

// Intentional fallthrough example — C++17 [[fallthrough]] suppresses the warning
switch (grade) {
    case 'A':
    case 'B':
        std::cout << "Pass";  // both A and B reach this
        [[fallthrough]];
    case 'C':
        std::cout << "Marginal";
        break;
}

A compact inline if/else that produces a value. Syntax: condition ? if_true : if_false

int max = (a > b) ? a : b;
// equivalent to:
// if (a > b) max = a;
// else       max = b;

goto instructs the program to jump to a labeled point in the code.

Start:
    // ...
    goto Start;  // jumps back to the label