Conditional Statements

Conditional Statements#

if-test#

We’ve already been using if-tests quite a bit. So let’s look a little more at their syntax:

if (condition1) {
   // do things if condition1 is true

} else if (condition2) {
   // do things if condition1 is false but condition 2 is true

} else {
   // do things only if both condition1 and condition2 are false

}

Tip

There is a form of an if-statement that does not use brackets if there is only a single statement to execute:

if (condition)
    statement;

This is potentially dangerous—if someone later edits the code and decides that they want to add another statement to that condition, they might do:

if (condition)
    statement;
    another_statement;

But since there are no braces, only statement is conditionally-executed. another_statement is not part of the if-test and will always be executed.

For this reason, it is always best to use brackets.

Note

C++17 also allows for a form with an initializer before the conditional (e.g., to open a file). We will not explore this here.

Tip

There is also a simple ternary operator in C++ of the form:

condition ? true-result : false result

Where true-result is the value used if condition is true and false-result otherwise.

For instance:

int i{10};

double x = (i > 5) ? 1.0 : 0.0;

switch statement#

A switch statement takes action on a single expression, and has many different cases that can take different actions. For example:

int i{2};
std::string text{};

switch (i) {

   case 0:
       text = "zero";
       break;

   case 1:
       text = "one";
       break;

   case 2:
   case 3:
   case 4:
       text = "2 <= i <= 4";
       break;

   default:
       text = "i > 4";

}

Warning

Notice that each case region ends with break. If you omit the break, then the flow “falls through” to the next options.

Contents