C++ Switch

One value, several labels

A switch compares an integer (or an enum) against a list of case labels. When a label matches, execution jumps there. It is a menu: the program looks at one number and picks a branch.

You cannot switch on a string in standard C++. For text, use if / else if. For ranges such as score >= 80, use if as well. Switch wants exact matches.

A complete program

Each case ends with break; so the program leaves the switch after that branch.default runs when no label matches.

#include <iostream>
using namespace std;

int main() {
  int day = 3;
  switch (day) {
    case 1:
      cout << "Monday" << endl;
      break;
    case 2:
      cout << "Tuesday" << endl;
      break;
    case 3:
      cout << "Wednesday" << endl;
      break;
    default:
      cout << "another day" << endl;
      break;
  }
  return 0;
}

case, default, break

• case n: is a label. n must be a constant integer expression.
• default: is the fallback. Put it last. You can omit it if every value is covered.
• break; jumps out of the switch. Without it, execution continues into the next case.

The parentheses after switch hold the value you test. The braces after that hold every case. Case labels themselves do not use extra parentheses.

Fall-through

If you forget break, C++ does not stop at the end of that case. It keeps running the statements in the following cases until it hits a break or the closing brace. That is called fall-through. It is almost always a bug.

#include <iostream>
using namespace std;

int main() {
  int day = 1;
  switch (day) {
    case 1:
      cout << "Mon" << endl;
    case 2:
      cout << "Tue" << endl;
      break;
    default:
      cout << "other" << endl;
      break;
  }
  return 0;
}

Sharing one body

Stacking labels without statements between them is the one common, intentional fall-through. Several values run the same block. Put a comment on the empty cases so the next reader knows it is deliberate.

#include <iostream>
using namespace std;

int main() {
  int day = 6;
  switch (day) {
    case 6:
    case 7:
      cout << "weekend" << endl;
      break;
    default:
      cout << "weekday" << endl;
      break;
  }
  return 0;
}

switch versus if

Enums belong with switch. You will meet enum later; the shape is the same: one value, named cases, a break on each branch.

What to remember

• Switch on integers and enums, not strings.
• End each case with break unless empty labels share a body.
• Use default for unexpected values.

Next: while — repeating a block while a condition stays true.