const 常量（const 常量）.docVIP

const 常量（const 常量） 1) you can define const constants (2) const can modify the parameters of a function and return values Detailed content: 1, what is const? A constant type is a type that is specified by the type modifier const, and a constant type variable or object value is not updated. (of course, we can update: substitution) 2. Why introduce const? The initial purpose of const is to replace the precompiled instructions, eliminate its shortcomings, and inherit its advantages. 3, what are the main functions of cons? (1) you can define const constants that are immutable. Such as: Const int Max=100; int Array[Max]; (2) easy to type checking, so that the compiler has more understanding of the content and eliminates some pitfalls. For example: void f (const int i) {...}...... the compiler will know that I is a constant, not allowed to modify; (3) to avoid ambiguous figures, also can adjust and modify the parameters conveniently. As with macro definitions, you can do it without changing it! If (1), if you want to modify the contents of Max, only need: const, int, Max=you, want; you can! (4) you can protect what is modified, prevent accidental changes, and enhance the robustness of your program. For example, if the I is modified in the body of the function, the compiler will make a mistake; for example: Void, f (const, int, I) {i=10, //error} (5) provides a reference for function overloading. Class A {...... Void f (int i) {...} / / a function... Void f (int i const) {...} / /... A function overloading...... }; (6) saving space and avoiding unnecessary memory allocation. Such as: #define PI / / 3.14159 macro constant Const doulbe Pi=3.14159; / / at this time did not put Pi in the ROM...... Double i=Pi; / / Pi at this time for the allocation of memory, no longer assigned! Double I=PI; / / compile time performs macro substitution, memory allocation Double j=Pi; / / no memory allocation Double J=PI; / / then macro substitution again allocate memory! Const defines a constan