Chapter 4 Arrays & Strings about pointers in programming

about pointers in programming

1. 1 CHAPTER 4 Array and String

2. 2 A rrays in c++ Arrays are series of elements of the same type placed in continuous memory locations that can be individually referenced by adding an index to a unique name. The index value starts at 0 i.e., first value is referred . For example, an array that contain 4 integer values of type int called age could be represented this way:

3. Declaration of arrays in C++: 3 A TYPICAL DECLARATION FOR AN ARRAY IN C++ IS: Syntax : Data Type array_name [ array_size ]; where Data Type is a valid data type in c ++( int , float...), Array_Name is a valid array identifier and Array_Size : is enclosed within brackets [], specifies how many of these elements the array contains . Example : int data[ 5 ]; // 5 elements all are integers char ch [10];// 10 elements all are characters double x[100];// 100 elements all are double

4. Initializing array in c++ . 4   V arious types of initializations: int data[5]={ 16,2,77,120,9} //The number of elements in the array that we initialized within curly brackets { } must match with the array size. int data[ ]={16,2,77,120,9}; //size of the Array will be defined by the number of values included between curly brackets { }. int data[5]={16,2,77}// the rest of 2 values are 0 . int data[5]={0};// all element will be initialized 0.

5. 5 Arrays can be initialized, but they cannot be assigned : float a[7] = { 22.2,44.4,66.6 }; float b[7] = { 33.3,55.5,77.7 }; b=a ; //ERROR: arrays cannot be assigned! Nor can an array be used to initialize another array : float a[7] = { 22.2,44.4,66.6 }; float b[7] = a ; // ERROR: arrays cannot be used as initializers!

6. Accessing the values of an array . 6 Elements of an array are accessed using index .   Syntax: Array name[index ]; Index:- is position of each element in an array Array index is start from 0 To n-1 The first element is the 0 th element! If you declare an array of n elements, the last element is number at index n-1 . If you try to access element at index n it is error! Example:- assume da[5 ] ={16,2,77,120,9 } ; da[0] da[1] da[2] da[3] da[4] 16 2 77 120 9

7. 7 To access the first element in the given array we can do it by : da[0 ]; to assign the value 75 in the third element of da   da[2] = 75; and, to assign the value of the third element of data to a variable called a, we could write: a=data[2 ];

8. 8 // arrays example #include < iostream > using namespace std ; int x[] = {6 , 2, 7 , 4, 1}; int n, result=0; int main (){ for ( n=0 ; n<5 ; n++ ){ result += x[n]; } cout << result; return 0; } Output:20

9. Multidimensional Array 9 => Multidimensional Arrays :are arrays of arrays or arrays of two or more dimension. =>Used to work with data requiring multidimensional arrays. for example, matrices and data in the form of a table.

10. 10 Declaration To declare a 2D array, two size specifies are required: first one is for the number of rows and second one is for the number of columns. int a[3][5]; // 2D array Char x[3][5][9] //3D array Various Initialization options : int a[2][3]={{1,5,7},{2,3,6}}; int a[2][3]={0}; all array elements are 0. int a[2][3]={{1,5},{2}}

11. 11 Accessing the values of an array . To access a certain element indices or subscript corresponding to each dimension should be supplied. Each element in a 2D array is accessed with two subscripts: the first one is for its row and the second for its column . Example: int score[3][4];

12. 2-D Array Example 12 Example of multidimensional array #include< iostream.h > void main(){ int SomeArray [5][2] = {{0,0},{1,2}, {2,4},{3,6}, {4,8}} for ( int i=0; i<5; i++) for ( int j = 0; j<2;j++) { cout <<" SomeArray ["<<i<<"]["<<j<<'']: ''; cout << endl << SomeArray [i][ j]; } }

13. Strings in C++ 13 What are Strings ? In C++ string is a sequence of character . last character of a string is the null character ‘\0’. The null character indicates the end of the string. Examples of a strings are:

14. String declaration 14 To declare variables of type String : syntax: string string_name ; Example string fullname ; String initialization Strings are initialized by using double Quotation (“ ”). There are different ways of string initialization Example: Fullname =“ Abebe ”; String fullname =“ Abebe ”; String anathername = fullname ; //now both fullname and anothername hold Abebe .

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16. 16 Any array of character can be converted into string type in C++ by appending the null character at the end of the array sequence. Example: char name[20]; N.B 1.we need not initialize all the available space (20) 2.the string will terminate by the null character ‘\0’ Initialization char s1[] = "example"; char s2[20] = "another example“ would store the two strings as follows: s1 | e|x|a|m|p|l|e |\0| s2 | a|n|o|t|h|e|r | | e|x|a|m|p|l|e |\0|?|?|?|?| char my_string []={‘ H’,’e’,’l’,’l’,’o ’,’\0 ’} OR char my_string []=”Hello”; my_string [0]=’H’; my_string [3]=’l’; cout << my_string [2]; cout << my_string ; cin >> my_string ;

17. 17 With cin space will not be read. To read text containing blanks we use a function called cin.get () . Syntax: cin.get (Address to store input, Max length); Eg . // cin with strings #include < iostream > #include <string> using namespace std ; int main () { char mystr [100]; cout <<"What's your name? "; cin.get (mystr,100); cout <<"Hello "<< mystr << ".\n"; cout <<"What is your favorite team? "; cin.getl (mystr,100); cout <<"I like "<< mystr <<" too!\n"; return 0; }

18. String Manipulations functions 18 String length i) Strlen : returns the length of the string including the spaces without the null character ‘\0’; Syntax: strlen (Array/string name) ; #include < iostream > #include <string> using namespace std; int main () { char name[50]; cout <<"Enter Your Name:"" "; cin >>name; cout <<"The length of Your Name is"" "<< strlen (name)<< endl ; return 0; }

19. String concatenation 19 ii) strcat : concatenates or merges two strings Syntax: strcat (first string, second string); NB. 1.The first string hold the concatenated string 2.the size of the first string must be large enough to hold both strings. #include < iostream > #include <string> using namespace std; int main () { char str1[13]="Hello "; char str2[]="World!"; cout <<"Before: "<<str1<< endl ; cout << strcat (str1, str2)<< endl ; cout <<"After: "<<str1<< endl ; return 0; }

20. String compare 20 iii) strcmp : compares strings based on their alphabetical order . Syntax: strcmp (str1,str2) ; Alphabetical comparison rules: if the two strings are equal negative if the first string comes before the second in alphabetical order positive if the first string comes after the second in alphabetical order Example: #include < iostream > #include < cstring > void main() { cout << strcmp (" abc ", " def ") << endl ; cout << strcmp (" def ", " abc ") << endl ; cout << strcmp (" abc ", " abc ") << endl ; cout << strcmp (" abc ", " abcdef ") << endl ; cout << strcmp (" abc ", "ABC") << endl ;

21. String copy 21 iv) strcpy : is used to copy the second string to the first. This is because arrays can't be copied using the assignment operator (=). Syntax : strcpy (str1,str2); Example: char str1[20]; char str2[] = "Second String"; strcpy (str1, str2); cout <<"str1: "<<str1<< endl ; strcpy (str2, "Another String"); cout <<"str2: "<<str2<< endl ;

22. String/Numeric Conversion 22 i ) atoi =  string to int i ) itoa  int to string ii) atof =  string to float ii) ftoa float to string iii)atoll=  string to long iii) ltoa long to string

23. 23 Example: int num = atoi ("4123"); //num = 4123 long lnum = atol ("12345678"); float fnum = atof ("2.34");

24. 24 Syntax : string_name.length (); string_name.size ();

25. 25 Syntax : string_name.at(index);

26. 26 #include< iostream > #include<string> using namespace std; int main() { string n=“ Desalegn"; cout << n.at (0)<< endl ; cout << n.size ()<< endl ; cout << n.at ( n.size ()-1)<< endl ; return 0; } Example Using at

27. 27 Thank U !!!