CSCI 235

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Custom Types ​

Chapter 7

Type Aliasing ​

We can create new names for existing types with the keyword using or typedef.

  • Syntax (two options):

    cpp
    typedef existingTypeName newTypeName; // traditional method
using newTypeName = existingTypeName; // preferred in the new standard

  • An example that creates a new name, Number, for the int type.

    cpp
    using Number = int; // Create a new name for the int type

const Number MAX = 100; // Define a new const int using the new type name

  • These statements do NOT create any new data types. They create only aliases to existing types.

Auto Variable Types ​

C++11 and beyond allow auto declaration of variables.

  • Data type does not need to be specified when initializing a variable at declaration.

    cpp
    auto num1 = 15;   // num1 is an int because 15 is an int.
auto num2 = 15.0; // num2 is a double
auto num3 = 'A';  // num3 is a char
auto num4 = num1; // num4 is an int

  • The auto keyword is a placeholder for a type, but it is not itself a type. The compiler determines the type based on the value it receives.

  • There is no conversion between types, so your code is not only more flexible but more efficient.

  • The variable must be initialized at declaration. For example, the following code will not compile.

    cpp
    auto value; // compiler error
value = "Test";