CSE 100 Lecture Notes - Lecture 33: Array Data Structure, Bounds Checking, In C
27 Apr 2018
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Chapter 8
● Array subscripts
○ can be an integer constant, integer variable, of integer expression
○ Examples →
■ cin >> tests[3]; (int constant)
■ cout << tests[i]; (int variable)
■ cout << tests[i+j]; (int expression)
○ Accessing All Array Elements
■ to access each element of an array
● Use a loop
● Let the loop control variable be the array subscript
● A different array element will be referenced each time through the
loop
● for(i=0; i<5; i++)
● cout << tests[i] << endl;
○ Getting Array Data from a File
■ const int ISIZE = 5;
■ int sales [ISIZE];
■ ifstream dataFile;
■ dataFile.open(“sales.dat”);
■ if(!dataFile)
● cout << “Error opening data file\n;
■ else // Input daily sales
■ { for (int day = 0; day < ISIZE; day++)
● dataFile >> sales[day];
■ dataFile.close();
■ }
○ Sending Array Data to a File
■ Open the file using an ofstream object
■ Use a loop to write each array element to the file
■ Close the file
● No bounds checking
○ There are no checks in C++ that an array subscript is in range
○ An invalid array subscript can cause the program to overwrite other memory
○ Example →
■const int ISIZE = 3;
■int i = 4;
■int num[ISIZE];
■num[i] = 25;
■
[0]
[1]
[2]
25
■ ^^^^^^num^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
○ Off by One Erros
■ These most often occur when program accesses data one position
beyond the end of an array, or misses the first or last element of an array
■ If an array has size n, then the subscripts range from 0 to n-1
● 8.4 Array Initialization
○ An array can be initialized during program execution with assignment statements
■ tests[0] = 79;
■ tests[1] = 82; //etc
○ It can be initialized at array definitioj with an initialization list
■ const int ISIZE = 5;
■ int tests[ISIZE] = {79,82,91,77,84};
○ Start at element 0 or 1?
■ You may choose to declare arrays to be one larger than needed. This
allows you to use the element with subscript 1 as the ‘first’ element, etc.,
and may minimize off by one errors
■ The element with subscript 0 is not used
■ This is most often done when working with ordered data e.g. months of
the year or days of the week
○ Partial Array Initialization
■ If array is initialized at definition with fewer values than the size declarator
of the array, the remaining elements will be set to 0 or the empty string
● int tests[ISIZE] = {79, 82};
●
79
82
0
0
0
■ Initial values are used in order; you cannot skip over elements to initialize
a noncontiguous range
■ You cannot have more values in the initialization list than the declared
size of the array
● Implicit Array Sizing
○ C++ can determine the array size by the size of the initialization list
○ short quizzes[ ] = {12, 17, 15, 11};
○
12
17
15
11
○
○ You must use either array size declarator or an initialization list when the array is
defined
○ Alternate Ways to Initialize Variables
■ You can initialize a variable at definition time using a functional notation
■ int length(12); // same result as int length = 12;
■ In C++ 11 and higher, you can also do this:
