If...Else

If...Else

Sometimes you want one thing when a condition is true, and something different when it is false. That is the job of the else branch.

The shape

if (condition) {
  // runs when the condition is true
} else {
  // runs when the condition is false
}

A time-of-day example

#include <iostream>
using namespace std;

int main() {
  int time = 20;
  if (time < 18) {
    cout << "Good day." << endl;
  } else {
    cout << "Good evening." << endl;
  }
  return 0;
}

Here time is 20, so time < 18 is false. The else branch runs and prints "Good evening."

When does the else run?

Exactly whenever the if condition is false. The two branches are opposites:

• Condition true: the if block runs.
• Condition false: the else block runs.

Never both, never neither

For any single if/else, exactly one of the two blocks runs. The program has no other path it can take.

TL;DR

• if (condition) { ... } else { ... } gives two alternative paths.
• The else block runs only when the condition is false.
• Exactly one branch runs each time.
• The else handles the "everything else" cases.