COIT29222-Structured Programming Lecture Week 08  Reading: Textbook (4 th Ed.), Chapter 4 Textbook (6 th Ed.), Chapter 7 Study Guide Book 2, Module 11  This week, we will cover the following topics:  Introduction to Character Arrays  Declaring & Initialising Character Arrays  Accessing Character Arrays  String Functions  Two Dimensional Arrays

Array of Characters - Strings  In C++, names, titles, messages, etc, can be held as an array of characters - the term string describes this type of data  In C++, the null character marks the end of a string (the “character” with value 0 in the ASCII coding system - '\0' in C++)  As such, character arrays to hold strings must be declared one element larger than the longest string they will hold

Strings  Newer Compilers eg Visual C #include string myName = “Sue Smith”;  Older Compilers eg Borland Turbo C++ #include char myName[20] = “Sue Smith”;

 The following statement declares an array of characters (MyName) that can hold a string containing up to five characters (including a null character) char MyName[5];  The following statements declare a constant (Size) and an array of characters (Address) that can hold a string containing up to ten characters const int Size=20; char Address[Size]; Declaring Character Arrays

 The following statements declare an array holding four characters – the last being the null character char Company[4] = {'I','B','M','\0'}; char Company[4] = "IBM"; char Company[] = "IBM";  In last two, a C++ string is used to initialise the array – note use of double quotes Initialising Character Arrays

 Initialising an array to the empty string can be achieved by: char Company[25] = "\0"; char Company[25] = {‘\0'};  The former is commonly used Initialising Character Arrays

 If no room is left for the null character, unexpected results/error can be expected char Array1[3] = "111";//Some compilers will give an //error: array bounds overflow error char Array2[3] = "22";//OK char Array3[3] = "33“;//OK  A character array can be printed with cout<<  The statement below cout << “Array2: “ << Array2; will print the following output Initialising Character Arrays Array2: 22

Character Arrays-Example  The following program will print out “Bill” #include void main() { char Name[]=“Bill"; for (int i=0; Name[i] != '\0'; i++) cout << Name[i]; cout << endl; }

Character Arrays-Example  The following program will print out “lliB” #include void main() { char Name[]=“Bill"; for (int i=2; i>=0; i--) cout << Name[i]; cout << endl; }

Character Arrays-Example #include const int size=10; void main() { char Name[size]="ihgfedcba“; char temp; for (int i=0; i<size-1; i++) for (int j=0; j<size-2; j++) if (Name[j]> Name[j+1]) { temp=Name[j]; Name[j]=Name[j+1]; Name[j+1]=temp; } cout << Name << endl; } What does this program do? Output: abcdefghi

String Input and Output  Output is as expected, input is not… #include void main (void) { char Sentence[80] = "\0"; cout "; cin.getline(Sentence,80); cout << ”Sentence: ” << Sentence << endl; }  cin >> stops accepting input when it meets a white space character – getline does not

String Input and Output  Notice that… #include void main (void) { char Sentence[80] = "\0"; cout "; cin.getline(Sentence,80); cout << ”Sentence: ” << Sentence << endl; }  up to 79 characters will be assigned to Sentence – position 79 will hold the null character

getline( ) Function getline(InputArray,ArraySize,UntilChar);  InputArray is a character array variable that will receive the input characters  ArraySize is an integer expression stating the size of the array – (a maximum of ArraySize–1 characters will be assigned to array, followed by null)  UntilChar is an optional parameter; if this character is encountered, input is terminated (‘\n’ is the default)

Other Issues  We cannot simply assign the contents of one character array to another: CharArray1 = CharArray2;  Or combine two character arrays CharArray1 = CharArray2 + CharArray3;  Or compare two character arrays: if (CharArray1 == CharArray2)  Use standard library functions instead

string Library Functions  Assignment and comparison of character arrays is can be accomplished using strcpy(Str1,Str2); // Str2 is copied to Str1 strcat(Str1,Str2); // Str2 is joined to Str1 strcmp(Str1,Str2); // Str2 is compared to Str1 strlen(Str1); // length of Str1  To use these functions, your program must include the string library: #include

strcpy( ) Function Example #include void main (void) { char Array1[] = "111"; char Array2[] = "222"; cout << "Array1: " << Array1 << endl; strcpy(Array1,Array2); cout << "Array1: " << Array1 << endl; } Array1: 111 Array1: 222

strcat( ) Function Example #include void main (void) { char Array1[] = "111"; char Array2[] = "222"; char Array3[7] = "333"; cout << "Array3: " << Array3 << endl; strcat(Array3,Array2); cout << "Array3: " << Array3 << endl; } Array3: 333 Array3:

strcmp( ) Function Example  Using this Compare function void Compare(char Array1[], char Array2[]) { char Relationship = '='; // establish relationship between strings if (strcmp(Array1,Array2) < 0) Relationship = '<'; else if (strcmp(Array1,Array2) > 0) Relationship = '>'; // report relationship between strings cout << "Array1(" << Array1 << ") " << Relationship << " Array2(" << Array2 << ")" << endl; }

strcmp( ) Function Example  The program below #include void Compare(char Array1[], char Array2[]); void main (void) { Compare("111","222"); Compare("111","122"); Compare("abc","ABC"); Compare("ABC","ABC"); Compare("ABCD","ABC"); }

strcmp( ) Function Example  Produces the following output…  Comparison is made using the ASCII value on characters in the string Array1(111) < Array2(222) Array1(111) < Array2(122) Array1(abc) > Array2(ABC) Array1(ABC) = Array2(ABC) Array1(ABCD) > Array2(ABC)

ctype Library Functions  Other useful functions for handling characters and strings are: toascii(Char); // returns ACSII code for char toupper(Char); // returns upper case of char tolower(Char); // returns lower case of char  To use these functions, your program must include the ctype library: #include

toascii( ) Function Example #include void main (void) { cout << "code for 1 is: " << toascii('1') << endl; cout << "code for 2 is: " << toascii('2') << endl; cout << "code for a is: " << toascii('a') << endl; cout << "code for A is: " << toascii('A') << endl; } code for 1 is: 49 code for 2 is: 50 code for a is: 97 code for A is: 65

toupper( ) Function Example #include void main (void) { cout << "upper case of a is: " << toupper('a') << endl; cout << "upper case of a is: " << char (toupper('a')) << endl; cout << "upper case of 1 is: " << char (toupper('1')) << endl; cout << "upper case of A is: " << char (toupper('A')) << endl; } upper case of a is: 65 upper case of a is: A upper case of 1 is: 1 upper case of A is: A

Declaring Two-Dimensional Arrays  The following statement declares a two dimensional array (matrix) that can hold 9 integer values int matrix [3] [3];  matrix – rows & columns: column 0column 1column 2 row 0 matrix[0][0] row 1 row 2 matrix[2][2]

Initialising Two-Dimensional Arrays  int matrix[4][3] = { { 5, 2, 3}, { 4, 2, 6}, { 1, 1, 1}, { 2, 1, 4} };  The declaration double matrix[4][3] = {5}; initialises matrix[0][0] to 5 and all remaining elements to 0.  The declaration double matrix[4][3] = {1, 2, 3, 4}; initialises matrix[0] [0] to 1, matrix[0][2] to 3, matrix[1][0] to 4 and all remaining elements to zero.

Example-add matrix 1 and matrix 2 # include void main () { int matrix1[3][2] = { { 1, 2}, { 6, 2}, { 4, 5}}; int matrix2[3][2] = { { 2, 4}, { 3, 2}, { 4, 1}}; int matrix_res[3][2]; for (int rcount=0; rcount<3; rcount++) { for (int ccount=0;ccount<2; ccount ++) { matrix_res[rcount][ccount]=matrix1[rcount][ccount] + matrix2[rcount][ccount]; cout<< matrix_res[rcount][ccount]; } cout << endl; }

Summary  Character arrays are used to hold strings  Strings terminate in a null zero  So arrays must be of sufficient size to hold the characters in the string, plus one  Many library functions exist to handle strings, eg. strcat, strcpy, strlen, etc.  Newer compilers use the string library  Older compilers use string.h