1 Arrays and Strings Lecture: 25 19.09.2012 2 Design Problem l Consider a program to calculate class average Why?? ? - презентация

1

2 1 Arrays and Strings Lecture:

3 2 Design Problem l Consider a program to calculate class average Why?? ?

4 3 Add to Design Problem l Now your client says, I need to ALSO calculate and display deviations from the average Describe why this will or will NOT work

5 4 l Enter in the scores again l Use 100 separate variables » and cout and cin commands l Read (then re-read) from a file l The real answer … Possible Solutions Use arrays !!

6 5 Simple vs Structured Data Types l Simple data type => data element contains a single value l Structured data type => a data element contains a collection of data values x : 15 avg : ch : A scores : name : C L Y D E

7 6 Arrays l Arrays are Structured Data Types l They have a means of accessing individual components l Values can be retrieved from and stored in the structure scores : cout << scores[2]; scores[0] = 100;

8 7 One Dimensional Array l Structured collection of components » All of the same type l Structure given a single name l Individual elements accessed by index indicating relative position in collection l Type of elements stored in an array can be just about anything l Index of an array must be an integer

9 8 Use of Array for Our Problem l Store elements in array as read in l Go back and access for deviations Note declaration

10 9 Declaring Arrays l Syntax: Data_type Array_name [constant]; l Note declaration from our example Tells how many elements set aside

11 10 Declaring Arrays l Example specifies an array… » each element is an integer » there is space for 100 elements » the are numbered 0 through 99 scores :

12 11 Accessing Individual Components l Use the name of the array l Followed by an integer expression inside the square brackets [ ] scores : max = scores[0]; for (x = 0; x max) max = scores[x]; Index can be: - constant - variable - expression MUST be an integer

13 12 Out of Bounds Index l What happens if … l C++ does NOT check for index out of range l Possible to walk off into far reaches of memory -- clobbers... » other variable locations ».exe code » the operating system (??) float f_list [50]; f_list [100] = ; float f_list [50]; f_list [100] = ;

14 13 Initializing Arrays in Declarations l Possible to declare the size & initialize l Possible to omit size at declaration » Compiler figures out size of array int results [5] = {14, 6, 23, 8, 12 } float prices [ ] = { 2.41, 85.06, 19.95, 3.91 }

15 14 Arrays as Parameters l This is one task that CAN be done to the WHOLE array l C++ always passes arrays by reference

16 15 Arrays as Parameters l The name of the array is a pointer constant l The address of the array is passed to the function l Size of the array also passed to control loop

17 16 Arrays as Parameters l Note the empty brackets in parameter list » A number can be placed here but it will be ignored

18 17 Multidimensional Arrays l A collection of a fixed number of components arranged in two dimensions » All components are of the same type l The syntax for declaring a two-dimensional array is: dataType arrayName[intexp1][intexp2]; where intexp1 and intexp2 are expressions yielding positive integer values.

19 18 Multidimensional Arrays The two expressions intexp1 and intexp2 specify the number of rows and the number of columns, respectively, in the array l Two-dimensional arrays are sometimes called matrices or tables

20 19 Multidimensional Arrays double sales[10][5];

21 20 Accessing Array Elements l The syntax to access a component of a two- dimensional array is: arrayName[indexexp1][indexexp2] where indexexp1 and indexexp2 are expressions yielding nonnegative integer values indexexp1 specifies the row position and indexexp2 specifies the column position

22 21 Accessing Array Elements sales[2][3] = 35.60; 35.60

23 22 2-DIM. Array Initialization l Like one-dimensional arrays » Two-dimensional arrays can be initialized when they are declared l To initialize a two-dimensional array when it is declared 1. Elements of each row are enclosed within braces and separated by commas 2. All rows are enclosed within braces 3. For number arrays, if all components of a row are not specified, the unspecified components are initialized to zero

24 23 2-DIM. Array Initialization l Example: int anArray[3][5] = { { 1, 2, 3, 4, 5, }, // row 0 { 6, 7, 8, 9, 10, }, // row 1 { 11, 12, 13, 14, 15 } // row 2 };

25 24 2-DIM. Array Initialization l Accessing all of the elements of a two-dimensional array requires two loops: one for the row, and one for the column. l Since two-dimensional arrays are typically accessed row by row, generally the row index is used as the outer loop. for (int nRow = 0; nRow < nNumRows; nRow++) for (int nCol = 0; nCol < nNumCols; nCol++) cout << anArray[nRow][nCol];

26 25 Multidimensional Arrays l A collection of a fixed number of elements (called components) arranged in n dimensions (n >= 1) l Also called an n-dimensional array l General syntax of declaring an n-dimensional array is: dataType arrayName[intExp1][intExp2]...[intExpn]; where intExp1, intExp2, … are constant expressions yielding positive integer values Example: 3-Dimensional array: int anArray[5][4][3];

27 26 C-Strings or Character Arrays l We have learned that the elements of an array can be just about anything l Consider an array whose elements are all characters » Called a C-String » Has a collection of special routines

28 27 C-Strings or Character Arrays l Character array: An array whose components are of type char l String: A sequence of zero or more characters enclosed in double quote marks l C-stings are null terminated (\0) l The last character in a string is the null character

29 28 C-Strings or Character Arrays char str[80] = Amanuensis

30 29 C-Strings or Character Arrays There is a difference between 'A' and "A" » 'A' is the character A » "A" is the string A Because strings are null terminated, "A" represents two characters, 'A' and '\0 Similarly, "Hello" contains six characters, 'H', 'e', 'l', 'l', 'o', and '\0'

31 30 C-Strings or Character Arrays l Consider the statement char name[16]; l Because C-strings are null terminated and name has sixteen components » the largest string that can be stored in name is 15 If you store a string of length, say 10 in name » the first 11 components of name are used and the last 5 are left unused

32 31 Declaration of C-Strings Similar to declaration of any array char name[30]; // no initialization char title [20] = "Le Grande Fromage"; // initialized at declaration // with a string char chList [10] = {'a', 'b', 'c', 'd'}; // initialized with list of char // values

33 32 Initializing Strings l When a character array is declared, it is legal to use the assignment operator to initialize l Note : use of the = operator only legal for char array initialization l But : aggregate array assignment is NOT greeting = dont do it;

34 C-Strings: Example-1 #include using namespace std; int main() { const int MAX = 80; //maximum characters in a string char str[MAX]; //string variable str cout<< Enter a string \n; cin>>str; //put string in str cout<< You entered: << str << endl; //display string from str getch(); return 0; } 33

35 Reading Embedded Blanks #include using namespace std; int main() { const int MAX = 80; char str[MAX]; cout<< Enter a string \n; cin.get(str,MAX); //member function get() of the stream class of // which cin is an object cout<< You entered: << str << endl; getch(); return 0; } 34

36 Reading Multiple Lines #include using namespace std; const int MAX = 2000; char str[MAX]; int main() { cout<< Enter a string \n; cin.get(str, MAX, $); //terminate with $ cout<< You entered: << str << endl; getch(); return 0; } 35

37 Copying a string: Hard-way #include #include // for copying a string #include using namespace std; int main() { char str1[] = C++ is the best programming language that I have ever used.; const int MAX = 80; char str2[MAX]; for(int j=0; j < strlen(str1); j++) str2[j] = str1[j]; cout<< str2 << endl; getch(); return 0; } 36

38 Copying a string: Easy-way #include #include // for copying a string #include using namespace std; int main() { char str1[] = C++ is the best programming language that I have ever used.; const int MAX = 80; char str2[MAX]; strcpy(str2, str1); cout<< str2 << endl; getch(); return 0; } 37

39 Standard C++ string Class 38 #include #include //string class #include using namespace std; int main() { string s1(Man); string s2 = Beast; string s3; s3 = s1; //assign cout << s3 = << s3 << endl; s3 = Neither + s1 + nor ; //concatenate s3 += s2; //concatenate cout << s3 = << s3 << endl; s1.swap(s2); //swap s1 and s2 cout << s1 << nor << s2 << endl; getch(); return 0; }

> s; cin.getline(s,'\n'); cout << s; Assignment is illegal char cs[30]; cs = "don't do it"; l Comparisons not allowed " title="39 Contrast/Compare Strings and C-Strings Assignment is OK string s; s = "hi mom"; Comparison OK if (s < "geek") … I/O allowed cin >> s; cin.getline(s,'\n'); cout << s; Assignment is illegal char cs[30]; cs = "don't do it"; l Comparisons not allowed " class="link_thumb"> 40 39 Contrast/Compare Strings and C-Strings Assignment is OK string s; s = "hi mom"; Comparison OK if (s < "geek") … I/O allowed cin >> s; cin.getline(s,'\n'); cout << s; Assignment is illegal char cs[30]; cs = "don't do it"; l Comparisons not allowed l I/O allowed much the same way > s; cin.getline(s,'\n'); cout << s; Assignment is illegal char cs[30]; cs = "don't do it"; l Comparisons not allowed "> > s; cin.getline(s,'\n'); cout << s; Assignment is illegal char cs[30]; cs = "don't do it"; l Comparisons not allowed l I/O allowed much the same way"> > s; cin.getline(s,'\n'); cout << s; Assignment is illegal char cs[30]; cs = "don't do it"; l Comparisons not allowed " title="39 Contrast/Compare Strings and C-Strings Assignment is OK string s; s = "hi mom"; Comparison OK if (s < "geek") … I/O allowed cin >> s; cin.getline(s,'\n'); cout << s; Assignment is illegal char cs[30]; cs = "don't do it"; l Comparisons not allowed ">

41 40 Working with Strings Functions provided in #include Used instead of assignment Used for comparisons

42 Working with Strings l C-strings are compared character by character using the collating sequence of the system l If we are using the ASCII character set 1. The string "Air" is smaller than the string "Boat" 2. The string "Air" is smaller than the string "An" 3. The string "Bill" is smaller than the string "Billy" 4. The string "Hello" is smaller than "hello" 41

43 Working with Strings 42

44 Passing Arrays to Functions Arrays can be used as arguments to functions. 43

45 Passing Arguments to Arrays #include using namespace std; int sum(int list[], int listSize) { int index, sum = 0; for(index=0; index