Switch Statements

There is another way to write conditionals in C++, and most other programming languages. It is called the switch statement. They’re most useful when we have a variable, and we want to do different things depending on the value of that variable.

Switch statements look something like this:

1#include <iostream>
2
3using namespace std;
4int Day{3};
5
6int main(){
7  switch (Day) {
8  case 1:
9    cout << "Monday";
10    break;
11  case 2:
12    cout << "Tuesday";
13    break;
14  case 3:
15    cout << "Wednesday";
16    break;
17  }
18}
19

In this example, we’re switching on the value of Day. Its value is 3, so we trigger the case 3: scenario, logging out Wednesday:

1Wednesday
2

Testing Multiple Values

If we want multiple values to trigger the same action, the syntax looks like this:

1#include <iostream>
2
3using namespace std;
4int Day{6};
5
6int main(){
7  switch (Day) {
8  case 1:
9    cout << "Monday";
10    break;
11  case 2:
12    cout << "Tuesday";
13    break;
14  case 6:
15  case 7:
16    cout << "Weekend";
17  }
18}
19

Here, we’re logging out Weekend if the value of Day is either 6 or 7. It is, so we get the expected output:

1Weekend
2

This is an example of fallthrough, a quirky characteristic of switch statements. In this case, the fallthrough was desired, but it’s often a source of bugs.

Fallthrough and break

The inclusion of the break keyword in the previous examples is to prevent fallthrough, which is the default behavior of switch statements.

Let's take a look at what happens if we don’t include the break statements:

1#include <iostream>
2
3using namespace std;
4int Day{1};
5
6int main(){
7  switch (Day) {
8  case 1:
9    cout << "Monday";
10  case 2:
11    cout << "Tuesday";
12  case 3:
13    cout << "Wednesday";
14  }
15}
16

Once a case statement is triggered, every subsequent case statement is also triggered, until we either reach the end of the switch statement or encounter a break instruction.

In this scenario, because the first case was triggered, and we have no break statements, the code in every case was executed. This generated the following output:

1MondayTuesdayWednesday
2

Fallthrough behavior is rarely useful, but it remains the default implementation of switch statements in C++, and most other programming languages.

So, we should be mindful of it and generally remember that, in most scenarios, we’ll need to add breaks to our switch statements.

Adding a default dase

Switch statements can have a default case, which is activated in all scenarios, unless a previously activated case triggered a break:

1#include <iostream>
2
3using namespace std;
4int Day{3};
5
6int main(){
7  switch (Day) {
8  case 1:
9    cout << "Monday";
10    break;
11  case 2:
12    cout << "Tuesday";
13    break;
14  default:
15    cout << "Something else";
16  }
17}
18

1Something else
2