Pascal Programming

Task 19 Searching Data

Searching refers to the problem of finding a particular element from a list.

Different Techniques of Searching

• Sequential Search ( Linear Search ) examines the data items in the order they appear in the list until the desired value is located or the end of the list is reached
• Ordered Sequential Search ( Ordered Linear Search ) is an improved version of Sequential Search
  • we need to continue the search only until the value of an element exceeds the search value (list sorted in ascending order)
• Binary Search requires that the list has been sorted and the list is cut in half repeatedly until the search value is found or the list is fully searched
• Sequential Search Vs Binary Search

  Sequential Search	Binary Search
  Simple algorithm and easy to implement	Algorithm rather complex
  The list need not be sorted	The list must be sorted
  Requires many comparisons	Requires very few comparisons
  Slow in locating a search value	Very fast in locating a search value

Using a Module Design technique to write a Pascal program to search for and print the details of stock items held by ABC Electric Appliance Company :

• get code table and stock information (by procedure readdata)
• search for items by sequential search (by procedure searchdata)
• display item details and calculate total stock value ( by procedure disptotal)

Below are the sample outputs of a Pascal program. In these outputs, the information in purple colour are entered through the keyboard by the user. All other items are output from the program.

The follwoing is the content of part of the stock information (fstock.dat) of the company.

Main Program

1. Declare the following Global Constants with suitable value within the main program
   • max_rec (to store the possible maximum number of records in the codified table)
2. Declare the following Global Variables within the main program with the suitable data type (integer, real , char or string[x])
   • code (a string array to store the code of the electric appliance and 3 characters in length) (e.g. C13)
   • item (a string array to store description of the electric appliance and 10 characters in length)
   • price (a real number array to store unit cost of each electric applicance)
   • qty (an integer array to store the quantity of each electric applicance)
   • stock (a real number array to store total value of each electric applicance in the stock)
   • no_of_items (to store number of items in the current list)
   • reply (to store response of the question ' More searching (Y/N) : ')
3. Initialize corresponding arrays and count the number of items within the code table by calling the procedure readdata(no_of_items).
4. Prompt the user to enter the serached code and display the details of the searched items by calling the procedure searchdata(no_of_items).
5. If no more searching is needed then display item details and calculate total stock value by calling the procedure disptotal(no_of_items).

Sub-program (procedure)

6. Details of the procedure readdata
   • Declaration of a procedure readdata
          procedure readdata ( var   n : integer );
          var fcode : text; {internal file variable used by the program}
          begin     {readdata}
             <prepare the source file for input>
             <read all data to the corresponding arrays>
             <count the number of items in the list>
             <close the source file>
          end;      {readdata}
7. Details of the procedure searchdata
   • Declaration of a procedure searchdata
          procedure searchdata ( n : integer );
          var searchcode : string; {to store the searched code value}
                valid , match : boolean;
                i , j : integer; {to act as loop counters}
          begin     {searchdata}
     
             {get searched value and check its length and format}
     
              repeat
                   <get the code number to be serached >
                   <check the length of the searched value>
                   if <its length is not correct> then
                        <set valid to false>
                   else
                        <check the format of the searched value>
                        if <correct format> then
                             <set valid to true>
                        else
                             <set valid to false>
              until valid ;
     
     
             {search and display matched items until the end of the list>}
     
             for i := 1 to n do
                  <set match to true> 
                  <set j to 1>
                  {compare the i^th code with the searchcode}
                  repeat
                       <check the j^th character of the searchcode and code>
                       <according the result of the j^th character checking>
                       <set match to false or increase j by one >
                  until (not match) or (j > 3);
     
                  if match then
                       <display the current i^th item's information>
     
             {end of for loop}
     
             {display the message ' Search Completed ! '}
     
          end;      {searchdata}
     
     
   • The procedure should accept only strings in the form of CNN where
     • C is either a letter A-Z or the symbol @ and
     • N is either a digit 0-9 or the symbol @
     • In the searching process, the subroutine should interpret the symbol @ as any letter or digit according to its position
8. Details of the procedure disptotal
   • Declaration of a procedure disptotal
          procedure disptotal ( n : integer );
          var total : real; {to store the total stock value}
                i : integer; {to act as loop counters}
          begin     {disptotal}
             <display item details and calculate total stock value>
          end;      {disptotal}
9. After coding, save your file as t19.pas at the drive S:\www\0507cit\programming\.
10. Execute your program and fix any problem occurred.