If-Else: One Decision Chooses One Path

The condition controls whether the if body runs

An if statement checks its condition before it runs any statement inside its if body. In this weather decision, isRaining has the value true, so the condition is true and the two output statements inside the braces run.

bool isRaining = true;

if (isRaining) {
    cout << "Take an umbrella" << endl;
    cout << "Wear boots" << endl;
} else {
    cout << "Leave the umbrella" << endl;
    cout << "Wear shoes" << endl;
}

cout << "Leave home" << endl;

Because isRaining is true, execution enters the if body. It prints "Take an umbrella" and then "Wear boots". The condition is evaluated before either output statement runs, so the value of the condition determines which body receives control.

Else is the false path of the same decision

The else body does not have its own condition. It is the path selected when the if condition is false. If the same assignment changes isRaining to false, execution skips the if body and enters the else body instead.

bool isRaining = false;

if (isRaining) {
    cout << "Take an umbrella" << endl;
    cout << "Wear boots" << endl;
} else {
    cout << "Leave the umbrella" << endl;
    cout << "Wear shoes" << endl;
}

cout << "Leave home" << endl;

With the false value, the weather messages are "Leave the umbrella" and "Wear shoes". An if-else pair has two possible bodies, but one evaluation of its condition selects exactly one of them. The selected body runs, and the other body does not run.

Braces, not indentation, decide which statements belong to a branch

Both weather messages belong to each branch, so each pair needs braces. Braces mark the complete body. Without them, an if or else controls only the next statement, even if the following statement is indented to look as though it belongs there.

if (isRaining)
    cout << "Take an umbrella" << endl;
    cout << "Wear boots" << endl;
else {
    cout << "Leave the umbrella" << endl;
    cout << "Wear shoes" << endl;
}

In the unbraced true branch, only the first output statement is controlled by if. The "Wear boots" statement is outside that body, despite its indentation. In this exact arrangement, the else also no longer attaches correctly, so the code produces a syntax error. Even when the code remains syntactically valid, misleading indentation can make an unconditional statement look conditional.

if (isRaining)
    cout << "Take an umbrella" << endl;
    cout << "Wear boots" << endl;
else {
    cout << "Leave the umbrella" << endl;
    cout << "Wear shoes" << endl;
}

Execution continues after either branch

The decision chooses a path temporarily. With isRaining true, the if body prints its two messages, then control leaves the braces and reaches "Leave home". With isRaining false, the else body prints its two messages, then control reaches that same statement. The decision does not stop execution after the selected body.