• Visual Studio C++ 2005
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4 Arrays, Strings, and Pointers So far, you have covered all the fundamental data types of consequence and you have a basic knowledge of how to perform calculations and make decisions in a program. This chapter is about broadening the application of the basic programming techniques that you have learned so far, from using single items of data to working with whole collections of data items. Chapter 4 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; I’ll refer to single items of data as data elements.

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You know how to create a single character in a variable of type char, a single integer in a variable of type short, type int, type long, or a single floating point number in a variable of type float or of type double. The most obvious extension to these ideas 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. Here’s an example of where you might need this. 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. 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. Of course, you would also need some means of picking out a particular employee from the whole bunch, together with the data from the generic variables associated with them. This kind of requirement arises with any collection of like entities that you want to handle in your program, whether they’re baseball players or battleships.

Microsoft usb driver version 5.1.2600.0. Naturally, C provides you with a way to deal with this. Arrays The basis for the solution to all of these problems is provided by the array in ISO/ANSI C. 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.

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The employee names in a payroll program could be stored in one array, the pay for each employee in another, and the tax due for each employee could be stored in a third array. Individual items in an array are specified by an index value which is simply an integer representing the sequence number of the elements in the array, the first having the sequence number 0, the second 1, and so on. You can also envisage the index value of an array element as being an offset from the first element in an array. The first element has an offset of 0 and therefore an index of 0, and an index value of 3 will refer to the fourth element of an array. For the payroll, you could arrange the arrays so that if an employee’s name was stored in the employeeName array at a given index value, then the arrays pay and tax would store the associated data on pay and tax for the same employee in the array positions referenced by the same index value. The basic structure of an array is illustrated in Figure 4-1.

Figure 4-1shows an array. The name height has six elements, each storing a different value. These might be the heights of the members of a family, for instance, recorded to the nearest inch. Because there are six elements, the index values run from 0 through 5.

To refer to a particular element, you write the array name, followed by the index value of the particular element between square brackets. The third element is referred to as height2, for example. If you think of the index as being the offset from the first element, it’s easy to see that the index value for the fourth element will be 3, for example.

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. Arrays, Strings, and Pointers Index value Index value for the 2nd element for the 5th element Array name Array name height0 height1 height2 height3 height4 height5 73 62 51 42 41 34 The height array has 6 elements. Figure 4-1 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: long height6; Because each long value occupies 4 bytes in memory, the whole array requires 24 bytes. Arrays can be of any size, subject to the constraints imposed by the amount of memory in the computer on which your program is running. 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: double cubicinches10; // Engine size double horsepower10; // Engine power output If auto mechanics are your thing, this would enable you to store the cubic capacity and power output of up to 10 engines, referenced by index values from 0 to 9.

As you have seen before with other variables, you can declare multiple arrays of a given type in a single statement, but in practice it is almost always better to declare variables in separate statements. Try It Out 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: // Ex401.cpp // Calculating gas mileage #include. Arrays, Strings, and Pointers Enter odometer reading: 26337 Do you want to enter another(y or n)? Y Enter gas quantity: 11.8 Enter odometer reading: 26598 Do you want to enter another(y or n)? N 1.Gas purchased = 14.9 gallons resulted in 33.8926 miles per gallon. 2.Gas purchased = 11.8 gallons resulted in 22.1186 miles per gallon.

How It Works Because you need to take the difference between two odometer readings to calculate the miles covered for the gas used, you use the odometer reading only from the first pair of input values — you ignore the gas bought in the first instance as that would have been consumed during miles driven earlier. During the second period shown in the output, the traffic must have been really bad — or maybe the parking brake was always on. The dimensions of the two arrays gas and miles used to store the input data are determined by the value of the constant with the name MAX.

By changing the value of MAX, you can change the program to accommodate a different maximum number of input values. This technique is commonly used to make a program flexible in the amount of information that it can handle. Of course, all the program code must be written to take account of the array dimensions, or of any other parameters being specified by const variables. This presents little difficulty in practice, however, so there’s no reason why you should not adopt this approach. You’ll also see later how to allocate memory for storing data as the program executes, so that you don’t need to fix the amount of memory allocated for data storage in advance. Entering the Data The data values are read in the while loop. Because the loop variable count can run from 0 to MAX - 1, we haven’t allowed the user of our program to enter more values than the array can handle.

You initialize the variables count and indicator to 0 and ‘y’ respectively, so that the while loop is entered at least once. There’s a prompt for each input value required and the value is read into the appropriate array element. The element used to store a particular value is determined by the variable count, which is 0 for the first input. The array element is specified in the cin statement by using count as an index, and count is then incremented ready for the next value. After you enter each value, the program prompts for confirmation that another value is to be entered.

The character entered is read into the variable indicator and then tested in the loop condition. The loop will terminate unless ‘y’ or ‘Y’ is entered and the variable count is less than the specified maximum value, MAX. After the input loop ends (by whatever means), the value of count contains one more than the index value of the last element entered in each array.

(Remember, you increment it after you enter each new element.) This is checked in order to verify that at least two pairs of values were entered. If this wasn’t the case, the program ends with a suitable message because two odometer values are necessary to calculate a mileage value.

Visual Studio C++ 2005

Chapter 4 Character Arrays and String Handling An array of type char is called a character array and is generally used to store a character string. A character string is a sequence of characters with a special character appended to indicate the end of the string. The string terminating character indicates the end of the string and this character is defined by the escape sequence ‘ 0’, and is sometimes referred to as a null character, being a byte with all bits as zero. A string of this form is often referred to as a C-stylestring because defining a string in this way was introduced in the C language from which C was developed by Bjarne Stroustrup. This is not the only representation of a string that you can use — you’ll meet others later in the book. In particular, C/CLI programs use a different representation of a string and the MFC defines a CString class to represent strings. The representation of a C-stylestring in memory is shown in Figure 4-2.

Name4 String termination character Each character in a string occupies A l b e r t E i n s t e i n 0 one byte char name = “Albert Einstein”; Figure 4-2 Figure 4-2illustrates how a string looks in memory and shows a form of declaration for a string that I’ll get to in a moment. Each character in the string occupies one byte, so together with the terminating null character, a string requires a number of bytes that is one greater than the number of characters contained in the string.

You can declare a character array and initialize it with a string literal. For example: char moviestar15 = “Marilyn Monroe”; Note that the terminating ‘ 0’is supplied automatically by the compiler.

If you include one explicitly in the string literal, you end up with two of them. You must, however, allow for the terminating null in the number of elements that you allot to the array.

You can let the compiler work out the length of an initialized array for you, as you saw in Figure 4-1.Here’s another example: char president = “Ulysses Grant”; Because the dimension is unspecified, the compiler allocates space for enough elements to hold the initializing string, plus the terminating null character. In this case it allocates 14 elements for the array president. Of course, if you want to use this array later for storing a different string, its length (including the terminating null character) must not exceed 14 bytes. In general, it is your responsibility to ensure that the array is large enough for any string you might subsequently want to store. Arrays, Strings, and Pointers String Input The header file contains definitions of a number of functions for reading characters from the keyboard. The one that you’ll look at here is the function getline, which reads a sequence of characters entered through the keyboard and stores it in a character array as a string terminated by 0.

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You typically use the getline function statements like this: const int MAX = 80; // Maximum string length including 0 char nameMAX; // Array to store a string cin.getline(name, MAX, ‘ n’); // Read input line as a string These statements first declare a char array name with MAX elements and then read characters from cin using the function getline. The source of the data, cin, is written as shown, with a period separating it from the function name.

The significance of the arguments to the getline function is shown in Figure 4-3. Cin.getline( name, MAX, ‘ n’ ); Figure 4-3 Because the last argument to the getline function is ‘ n’(newline or end line character) and the second argument is MAX, characters are read from cin until the ‘ n’ character is read, or when MAX - 1 characters have been read, whichever occurs first. The maximum number of characters read is MAX - 1 rather than MAX to allow for the ‘ 0’ character to be appended to the sequence of characters stored in the array. The ‘ n’ character is generated when you press the Return key on your keyboard and is therefore usually the most convenient character to end input. You can, however, specify something else by changing the last argument. The ‘ n’ isn’t stored in the input array name, but as I said, a ‘ 0’ is added at the end of the input string in the array. You will learn more about this form of syntax when we discuss classes later on.

Meanwhile, we’ll just take it for granted and use it in an example. Try It Out Programming With Strings You now have enough knowledge to write a simple program to read a string and then count how many characters it contains. // Ex403.cpp // Counting string characters #include using std::cin.