main
The Operating system uses the value returned by main method to determine whether the program succeeded or failed. A return value of 0 indicates success.#include
This line is a preprocessor directive. Tell compiler that we need to use the iostream library. The name inside angle brackets is a header. Every program that uses a library facility must include associated header. The directive #include must be written _disibledevent=> int ival(1024); // direct-initialization int ival = 1024; // copy-initialization
many new C++ programmers are confused by the use of the = symbol to initialize a variable. It is tempting to think of initialization as a for of assignment. But initialization and assignment are different operations in C++. This concept is particularly confusing because in many other languages the distinction is irrelevant and and can be ignored. Moreover, even in C++ the distinction rarely matters until _disibledevent=> Despite the use of extern, this statement defines pi. Storage is allocated and initialized. An extern declaration may include an initializer _disibledevent=>double pi; // error: redefinition of pi
Non const variables are extern by default. To make a const variable accessible to other files we must explicitly specify that it is extern.
最新评论