The auto Keyword
The auto keyword automatically detects the type of a variable based on the value you assign to it.
It helps you write cleaner code and avoid repeating types, especially for long or complex types.
For example: Instead of writing int x = 5; , you can write:
auto x = 5; // x is automatically treated as
intStarting in C++11 , auto became a powerful way to let the compiler figure out the type based on the value you assign.
Example with Different Types
Here's an example showing how auto can be used to create variables of different types, based on the values you assign:
Example
// Creating auto variables auto myNum = 5; // int auto myFloatNum = 5.99f; // float auto myDoubleNum = 9.98; // double auto myLetter = 'D'; // char auto myBoolean = true; // bool auto myString = string("Hello"); // std::stringImportant Notes
- auto only works when you assign a value at the same time (You can't declare auto x; without assigning a value)
- Once the type is chosen, it stays the same. See example below:
auto x = 5; // x is now an int
x = 10; // OK - still an int
x = 9.99; // Error - can't assign a double to an intNote
In this tutorial, we usually use int , double , and other basic types when the type is simple and easy to see.
But for more complex types - like iterators and lambdas , which you will learn more about in a later chapter, we use auto to keep the code cleaner and easier to understand.