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erence is the one that we have been using all along and continue to use throughout the book. |
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By now, you have probably noticed that the ampersand (&) has several meanings in the C++ language. To avoid errors, it pays to keep these meanings distinct from each other. Below is a table that summarizes the different uses of the ampersand. Note that a prefix operator is one that precedes its operand(s), an infix operator lies between its operands, and a postfix operator comes after its operand(s). |
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| Position | Usage | Meaning | | Prefix | & Variables | Address-of operation | | Infix | Expression & Expression | Bitwise AND operation (mentioned, but not explored, in Chapter 10) | | Infix | Expression && Expression | Logical AND operation | | Postfix | DataType& | Data type (specifically, a reference type)
Exception: To declare two variables of reference type, the & is attached to the variable name: int &var1, &var2; |
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When programmers use C++ classes, it is often useful for class objects to create dynamic data on the free store. Let's consider writing a variation of the DateType class of Chapter 15. In addition to a month, day, and year, we want each class object to store a message string such as My birthday or Meet Al. When a client program prints a date, this message string will be printed next to the date. To keep the example simple, we'll supply only a bare minimum of public member functions. We begin with the class declaration for a Date class, abbreviated by leaving out the function preconditions and postconditions. |
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class Date
{
public:
void Print() const; // Output operation
Date( /* in */ int initMo, // Constructor
/* in */ int initDay,
/* in */ int initYr,
/* in */ const char* msgStr );
private:
int mo;
int day;
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