One Dimensional Arrays (Part2) Sorting Algorithms Searching Algorithms Character Strings The string Class. 1

2 Sorting Algorithms Sorting algorithms arrange the data into either ascending or descending order, based on the values in the array. Sorting algorithms: Selection sort

3 Selection Sort Algorithm Find minimum value, place it in the first position. Find next minimum value, place it in the second position. Continue doing this until you have placed the second to the largest value in the second to the last position.

4 Practice! Fill in the following table to show how the array is sorted into ascending order using the selection sort. arr[0] arr[1] arr[2] arr[3] arr[4] swap min and arr[0]

#include using namespace std; void display(int list[],int size); void sort(int list[],int size); int main(){ int list[ ]={5,3,12,8,1,9}; int n=6; cout<<"List before sorting: "<<endl; display(list, n); sort(list, n); cout<<"List after sorting: "<<endl; display(list, n); return 0; }//main //Display list void display(int list[],int size) { for(int i=0;i<size;i++) cout<<list[i]<<" "; cout<<endl; }//display //Sort the list void sort(int list[],int size) { int min,hold; for(int i=0;i<size-1;i++){ //find the index "min" for the element //with lowest value min=i; for(int k=i+1;k<size;k++) if(list[min]>list[k]) min= k; //Exachage list[min] with list[i] hold = list[min]; list[min] = list[i]; list[i] = hold; //Display sorting steps – to be removed cout<<"List in sort fun: i="<<i<<endl; display(list, size); }//for }//sort 5

int list[]={5,3,12,8,1,9};int list[]={29,45,18,51,36}; 6

7 Searching Unordered Lists Simple Sequential Search –Examine each element starting with the first one until: a match is found. end of the list is reached. Sequential search can be implemented as: –a function which returns true if item in the list, false if item is not in the list. –a function which returns the location of the item if found, or –1 if not found.

//Search function returns position if element found #include using namespace std; int search(int value, int list[], int size); int main( ){ int list[6]={5,3,12,8,1,9}; int element, index; cout<<"Enter an element"<<endl; cin>>element; index= search(element,list,6); if(index != -1) cout<<"Element "<<element<<" is in index "<<index<<endl; else cout<<"Element " <<element <<" is not in the list "<<endl; return 0; } int search(int value, int list[], int size){ for (int i=0;i<size;i++) if(value==list[i]) return i; //value is found in list at position i return -1; //value was not found in the list } 8

//search function using returns true if element was found otherwise returns false #include using namespace std; bool search(int value, int list[], int size, int& pos); int main( ){ int list[6]={5,3,12,8,1,9}; int element, index (-1); cout<<"Enter an element"<<endl; cin>>element; if(search(element,list,6, index)) cout<<"Element "<<element<<" is in index "<<index<<endl; else cout<<"Element " <<element <<" is not in the list "<<endl; return 0; }//main bool search(int value, int list[], int size, int& pos){ bool found=false; for (int i=0;i<size && !found;i++) if(value==list[i]){ found=true; pos=i; //value is found in list at position i } return found; }//search 9

10 C Style Character Strings A C style strings is defined as a sequence of characters, terminated by the null character. When declaring a character array to store a C style string, memory must be allocated for the null character ('\0'). Literal string constants are enclosed within double quote marks: "a string".

11 C Style String Input Recall that the input operator ( >>) skips whitespace. To input strings with embedded whitespace, the getline() function can be used as illustrated: char phrase[SIZE]; cin.getline(phrase, SIZE); The getline () function reads up to SIZE-1 characters from the input stream and will insert the null character. getline () is a member function of istream class

#include using namespace std; int main() { char line[100]; ifstream fin; fin.open("xp.txt"); if(fin.fail()){ cout<<"Error opening file xp.txt"<<endl; return 1; } while (fin) { fin.getline(line,100); cout<<line<<endl; }//while return 0; }//main 12

C STYLE STRINGS In C++, we can define C-Style strings as array of characters. C-Style string represents a string as an array of character ending with the null character ‘\0’ that indicates the end of the string elements. Examples C++: String std=“Ahmed”, col=“Engineering”; C-Style string: Examples char std[]={‘A’,’h’,’m’,’e’,’d’,’\0’}; char col[]={‘E’,’n’,’g’,’i’,’n’,’e’,’e’,’r’,’i’,’n’,’g’,’\0’}; ‘\0’ is the null character and occupies one element of the array but not counted in the size of the array. ‘\0’ denotes the end of the array elements. 13

C STYLE STRING FUNCTIONS The Standard C++ library contains a set of predefined functions that operate on C style strings. These functions are defined in the header file: cstring Commonly used string functions: –strlen(str): returns the length of the string str –strcpy(str1,str2): copies two strings str2 into str1 –strcat(str1,str2 ): appends a copy of str2 to the end of str1 –strcmp(): Compare two strings str1 and str2 14

15 Example: C Style Strings #include #include //strcmp(), strcpy(), strcat() uses namespace std; int main(){ char str1[30] = “Salim", str2[30] = “Ali"; char phrase[20] = "'s shirt was green", sentence[30]; if (strcmp (str1,str2) < 0) strcpy (sentence, str1);// puts “Salim" into sentence else strcpy (sentence,str2); // puts “Ali” into sentence strcat (sentence, phrase); //add phrase to sentence cout << "Sentence is: " << sentence << endl; return 0; }

16 The string class Functions defined in String class, i.e. #include The string class implements the concept of a character string. A string object can increase and decrease its size dynamically. Numerous operators and functions are defined in the string class.

String Class include declaring string objects string word="Engineering"; string word2; string member functions –size( ) : returns string length –empty( ): checks if the string is empty (true/false) –substr (int start, int len): returns a substring from the specified string –c_str(): converts string format to c string (array of chars) 17

String class operators relational operators == = concatenation + += assignment = 18

Example Using string Class #include using namespace std; int main() {string str1="Salem", str2=“Ali"; string phrase = "'s shirt was green", sentence; if (str1 < str2) sentence = str1;// puts “Salem" into sentence else sentence = str2; // puts “Ali” into sentence sentence += phrase; cout << "Sentence is: " << sentence << endl; return 0; } Sentence is: Ali's shirt was green 19