兰州理工大学研究生课程VC++课件4

Arrays
• The basis for the solution to all of these problems is provided by the array. • An array is simply a number of memory locations called array elements or simply elements, each of which can store an item of data of the same given data type, and which are all referenced through the same variable name.
– }
• // Output results from 2nd entry to last entry
– for (int i = 1; i < count; i++) – {
• cout << endl
– – – – << setw(2) << i << "." // Output sequence number << "Gas purchased = " << gas[i] << " gallons" // Output gas << " resulted in " // Output miles per gallon << (miles[i] - miles[i - 1]) / gas[i] << " miles per gallon.";
• Suppose that you needed to write a payroll program. • Using a separately named variable for each individual’s pay, their tax liability, and so on, would be an uphill task to say the least.
long height[6];
• Because each long value occupies 4 bytes in memory, the whole array requires 24 bytes.
• You can declare arrays to be of any type.
• For example, to declare arrays intended to store the capacity and power output of a series of engines, you could write the following:
• • • • • • • • • •
// EX04-01.cpp // Calculating gas mileage #include <iostream> #include <iomanip> using std::cin; using std::cout; using std::endl; using std::setw; int main() {
Declaring Arrays
• You declare an array in essentially the same way as you declared the variables that you have seen up to now, the only difference being that the number of elements in the array is specified between square brackets immediately following the array name. • For example, you could declare the integer array height, shown in the previous figure, with the following declaration statement:
– – – – – – – const int MAX(20); // Maximum number of values double gas[MAX]; // Gas quantity in gallons long miles[MAX]; // Odometer readings int count(0); // Loop counter char indicator('y'); // Input indicator while (('y' == indicator || 'Y' == indicator) && count < MAX) {
HANDLING MULTIPLE DATA VALUES OF THE SAME TYPE
• You already know how to declare and initialize variables of various types that each holds a single item of information. • The most obvious extension to the idea of a variable is to be able to reference several data elements of a particular type with a single variable name. • This would enable you to handle applications of a much broader scope.
double engine_size[10]; // Engine size in cubic inches double horsepower[10]; // Engine power output
Using Arrays
• As a basis for an exercise in using arrays, imagine that you have kept a record of both the amount of gasoline you have bought for the car and the odometer reading on each occasion. • You can write a program to analyze this data to see how the gas consumption looks on each occasion that you bought gas:
• • • • • • • cout << endl << "Enter gas quantity: "; cin >> gas[count]; // Read gas quantity cout << "Enter odometer reading: "; cin >> miles[count]; // Read odometer value ++count; cout << "Do you want to enter another(y or n)? "; cin >> indicator;
•= 1) // count = 1 after 1 entry completed – { // ... we need at least 2
• cout << endl << "Sorry - at least two readings are necessary."; • return 0;
• A much more convenient way to handle such a problem would be to reference an employee by some kind of generic name — employeeName to take an imaginative example — and to have other generic names for the kinds of data related to each employee, such as pay, tax, and so on.
• To refer to a particular element, you write the array name, followed by the index value of the particular element between square brackets.
• The amount of memory required to store each element is determined by its type, and all the elements of an array are stored in a contiguous block of memory.
4. Arrays,Strings,and Pointers
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WHAT YOU WILL LEARN IN THIS CHAPTER:
• • • • • • • • How to use arrays How to declare and initialize arrays of different types How to use the range-based for loop with an array How to declare and use multidimensional arrays How to use pointers How to declare and initialize pointers of different types The relationship between arrays and pointers How to declare references and some initial ideas on their uses