1. CS-161 Computer Programming Lecture 15 & 16: Arrays II
Fall 2014 (Sections A & B)
Saqib Rasheed

2. Reserve Arrays

3. Printing a Sequence in Order
This program reads five numbers and then prints them in reverse order:
Out Put
Enter 5 numbers: 20 30 40 50
In reverse order: 10

4. #include<iostream.h>
void main() {
const int SIZE=5;
int i,a[SIZE];
cout << "Enter " << SIZE << " numbers:\n";
for ( i=0; i<SIZE; i++)
cin >> a[i];
cout << "In reverse order: \n";
for ( i=SIZE-1; i>=0; i--)
cout << "\t" << a[i]<<endl; }

5. Copy Arrays

6. Copying Arrays Data types should be identical Size should be same
int a [ 10 ] ;
int b [ 10 ] ;

7. Copying Arrays To copy from array “ a ” to array “ b ” :
b [ 0 ] = a [ 0 ] ;
b [ 1 ] = a [ 1 ] ;
b [ 2 ] = a [ 2 ] ;
b [ 3 ] = a [ 3 ] ;
… … …
b [ 10 ] = a [ 10 ] ;

8. Copying Arrays
for ( i =0 ; i < 10 ; i ++ )
b [ i ] = a [ i ] ;

9. Adding Arrays

10. Adding 1 D a[0]=10 + b[0]=1 = add[0]=11 a[1]=11 + b[1]=2 = add[1]=13
Array Array 2 = Array 3
a[0]=10 + b[0]=1 = add[0]=11
a[1]=11 + b[1]=2 = add[1]=13
a[2]=12 + b[2]=3 = add[2]=15
a[3]=13 + b[3]=4 = add[3]=17
a[4]=14 + b[4]=5 = add[4]=19

11. Adding 1 D(code) #include<iostream.h> void main () {
float ar1[5], ar2[5],add[5];
int i;
cout<<"\nEnter the value for array 1\n";
for(i=0; i<=4; i++)
cout<<"Array 1 Index ["<<i<<"]=";
cin>>ar1[i]; }

12. Adding 1 D(code) cout<<"\nEnter the value for array 2\n";
for(i=0; i<=4; i++) {
cout<<"Array 2 Index ["<<i<<"]=";
cin>>ar2[i]; }
cout<<"\n\tArray 1 + Array 2 = Array 3\n";
add[i] = ar1[i] + ar2[i];
cout<<"\n\tSum at Index ["<<i<<"]="<<add[i];
cout<<endl;}

13. Searching Arrays

14. Searching Arrays: Linear Search
Search array for a key value
Linear search
Compare each element of array with key value
Start at one end, go to other
Useful for small and unsorted arrays
Inefficient
If search key not present, examines every element

15. Example (Array Search)
#include<iostream> using namespace std; void main () { const int size=10; int a[size]={ 5,6,1,8,3,7,2,10,9,4}; for(int k=0; k<size; k++) cout<<a[k]<<" "; cout<<endl; int searchKey; cout << "Enter integer search key: "; cin >> searchKey;

16. for( k=0; k<size; k++)
if (a[k]==searchKey)
cout<<"The element to be searched is found at index a["<<k<<"]";
cout<<endl; }

17. Passing Arrays to Functions

18. Passing Arrays to Functions
Specify name without brackets
To pass array myArray to myFunction
int myArray[ 24 ];
myFunction( myArray, 24 );
Array size usually passed, but not required
Useful to iterate over all elements

19. Passing Arrays to Functions
Arrays passed-by-reference
Functions can modify original array data
Value of name of array is address of first element
Function knows where the array is stored
Can change original memory locations
Individual array elements passed-by-value
Like regular variables
square( myArray[3] );

20. Passing Arrays to Functions
Functions taking arrays
Function prototype
void modifyArray( int b[], int arraySize );
void modifyArray( int [], int );
Names optional in prototype
Both take an integer array and a single integer
No need for array size between brackets
Ignored by compiler
If declare array parameter as const
Cannot be modified (compiler error)
void doNotModify( const int [] );

21. Example (Passing Array to Functions)
void function1(int [], int); void function2(int); void main () { const int size=5; int array[]={1, 2,3 ,4,5}; cout<<"Array elements before function call:"; for (int i=0; i<5;i++) cout<<array[i]<<" "; cout<<endl;

22. function1(array, 5);
cout<<endl;
cout<<"Array elements after function call\n";
for (i=0; i<size;i++)
cout<<array[i]<<" ";
cout<<"passing array element array[2] to the function\n";
cout<<"Before:"<<array[2]<<endl;
function2(array[2]);
cout<<"After:"<<array[2]<<endl; }

23. //function definitions
void function1(int a[],int size) { cout<<"Array elements in function call\n"; for (int i=0; i<size; i++) cout<<(a[i]*=2)<<" "; } void function2( int x) { cout<<"In Function:"; cout<<x*2<<endl;

24. Array Sorting

25. Sorting Arrays Sorting data Bubble sort
Important computing application
Virtually every organization must sort some data
Bubble sort
Several passes through the array (assume: elements are to be sorted in increasing order)
Successive pairs of elements are compared
If increasing order (or identical), no change
If decreasing order, elements exchanged
Repeat these steps for every element

26. Sorting Arrays Example:
Go left to right, and exchange elements as necessary
One pass for each element
Original:
Pass 1: (elements exchanged)
Pass 2:
Pass 3: (no changes needed)
Pass 4:
Pass 5:

27. Sorting Arrays Swapping variables What happened? Solution
int x = 3, y = 4;
y = x;
x = y;
What happened?
Both x and y are 3!
Need a temporary variable
Solution
int x = 3, y = 4, temp = 0;
temp = x; // temp gets 3
x = y; // x gets 4
y = temp; // y gets 3

28. Example (Array Sorting)
#include<iostream> using namespace std; void main () { const int size=10; int a[size]={ 5,6,1,8,3,7,2,10,9,4}; for(int k=0; k<size; k++) cout<<a[k]<<" "; cout<<endl;

29. int temp; //sorting process for ( int pass = 0; pass < size - 1; pass++ ) for ( int j = 0; j < size - 1; j++ ) // loop to control number of comparisons per pass if ( a[ j ] > a[ j + 1 ] ) { temp = a[ j ]; a[ j ] = a[ j + 1 ]; a[ j + 1 ] = temp; } cout<<"Sorted Array\n"; for( k=0; k<size; k++) cout<<a[k]<<" "; cout<<endl;

30. Character Arrays

31. Character Arrays
2 kinds of strings
C-Strings
Objects of String class

32. Contd… Strings Arrays of characters All strings end with null ('\0')
Examples
char string1[] = "hello";
Null character implicitly added
string1 has 6 elements
char string1[] = { 'h', 'e', 'l', 'l', 'o', '\0’ };
Subscripting is the same
String1[ 0 ] is 'h'
string1[ 2 ] is 'l'

33. Contd… Input from keyboard Printing strings Puts user input in string
char string2[ 10 ];
cin >> string2;
Puts user input in string
Stops at first whitespace character
Adds null character
If too much text entered, data written beyond array
Printing strings
cout << string2 << endl;
Does not work for other array types
Characters printed until null found

34. Example (C-String Variable)
#include<iostream> using namespace std; void main () { char a[20]; cout<<"Enter String\n"; cin>>a; cout<<"you entered "<<a<<endl; }

35. Example (String Constants)
#include<iostream> using namespace std; void main () { char question[] = "Please, enter your first name: "; char greeting[] = "Hello, "; char yourname [80]; cout << question; cin >> yourname; cout << greeting << yourname << "!"<<endl; }

36. Example (Reading Embedded Blanks)
#include<iostream> using namespace std; void main () { char question[] = "Please, enter your first name: "; char greeting[] = "Hello, "; char yourname [80]; cout << question; cin.get(yourname,80); cout << greeting << yourname << "!"<<endl; }

37. Reading Multiple Lines
#include <iostream> using namespace std; const int MAX = 2000; //max characters in string char str[MAX]; //string variable str int main() { cout << “\nEnter a string:\n”; cin.get(str, MAX, ‘$’); //terminate with $ cout << “You entered:\n” << str << endl; return 0; }

38. The string type
Like cout, the string type is not part of the C++ language itself, it is defined in a header file string.
To use it, we have to include the header file:
#include <string>
Note that we have to use <string>, not <string.h>
A variable of type string can contain a string like "Hello World".
The length of the string can change during the execution of the program.

39. The string type
No need to specify array size (responsibility of memory management)
A string variable is declared as follows:
string s1;
Declare a new string We can also initialize it with a value as follows:
string hello = "Hello World";
We can output the string as usual:
cout << hello << endl; // prints "Hello World"

40. Two strings can be concatenated
string aa, newstr; aa = 'A'; newstr = aa + " " + hello; // newstr == "A Hello World" newstr += "!!"; // newstr == "A hello World!!";

41. Example
#include<iostream> #include<string> using namespace std; void main () { string question = "Please, enter your first name: "; string greeting ("Hello, "); string yourname; cout << question; getline(cin, yourname); cout<<greeting+yourname<<endl; }

42. strlen, strcpy() & strcmp()
Strlen (array); tells the length of the array
Strcpy(destination, source); Copies the source values to the destination
Strcmp(str1, str2); compares two strings str1 & str2 and gives the integer value.
0 indicates the matching strings
Otherwise not same

43. String Operations
Strlen
Strcpy
Strncpy
Strcmp
Strcat

44. strlen Determine string length strlen(string);
Returns number of characters in string
Terminating null character is not included
in length

45. strlen #include <iostream.h> #include <string.h>
void main (void) {
char x [40], char y [40], z[40];
strcpy (x, "Pakistan");
strcpy (y, "USA");
strcpy (z, "Italy");
cout << "X length is =" << strlen (x) << endl;
cout << "Y length is =" << strlen (y) << endl;
cout << "z length is =" << strlen (z) << endl; }

46. Output

47. strcpy strcpy is used to copy one string into an other
strcpy(string1,string2);

48. strcpy #include <iostream.h> #include <string.h>
void main (void) {
char x [ ] = “Pakistan is a great country”;
char y [28];
strcpy (y, x );
cout << “X is = “ << x << “\n”;
cout << “Y is = “ << y << “\n”; }

49. Output

50. strcmp
strcmp is used to compare two strings
strcmp(string1,string2);

51. strcmp #include <iostream.h> #include <string.h>
void main (void)
{ int check;
char x [ ] = "Pakistan is a great country";
char y [ ] = "Pakistan is a great country";
char z [ ] = "Pakistan is a country";
char f [ ] = "pakistan is a great country";
check=strcmp (y, x ); //both strings are same
cout<<check; //check = 0
check=strcmp(y,z); //both strings are different, length of 1st > 2nd
cout<<check; //check = 1
check=strcmp(z,y); //both strings are different, length of 2nd > 1st
cout<<check; //check = -1
check=strcmp(f,y); //first characters of both strings are different }

52. Output

53. strcat appends a copy of the source string to the destination string
/* strcat example */ #include <stdio.h> #include <string.h> int main () { char str[80]; strcpy (str,"these "); strcat (str,"strings "); strcat (str,"are "); strcat (str,"concatenated."); puts (str); return 0; }

54. Output