In line 12, the auto keyword is used, which tells the compiler to infer the type of k based on the value that it's initialized with. A declaration must provide a type, unlike other languages such as JavaScript. In line 11, an error is raised because the name j hasn't been declared. std is the namespace in which the string class is declared. The name std::string is visible because it's introduced in the string header file, which is merged into the source file in line 1. In line 10, a variable named str of type std::string is declared. In those languages, functions and classes can be used before their point of declaration in a source file. This behavior is different from other languages such as C#. To fix the error, you can either move the entire definition of C before main or else add a forward-declaration for it. However, this declaration raises an error because C isn't declared until later in the program, and isn't forward-declared. In line 9, a variable named obj of type C is declared. The name f is visible to the compiler because of the forward declaration on line 3. On line 8, an integer i is declared and initialized with the value produced by the function f. On line 7, a const variable named pi is declared and initialized. On line 5, the main function is declared. Std::string str // OK std::string is declared in headerДЄuto k = 0 // OK. The following example shows some declarations: #include Variables should be declared as close as possible before the point at which they're used. You can't refer to a function or class that is declared at some later point in the compilation unit. In C++ the point at which a name is declared is the point at which it becomes visible to the compiler.

A declaration specifies a unique name for the entity, along with information about its type and other characteristics. Each of these entities must be declared before they can be used. A C++ program consists of various entities such as variables, functions, types, and namespaces.

Declaration