The first job is to count the number of records in the input file. Once we know this, we can set up an array of records to hold the data. Once we have this array dimensioned we can read the data in from the file.
Once the array is populated with data, we ask the user to enter a search term. The algorithm searches through the array linearly until the index to the required record is either found or the end of the array is reached. We can then do useful things with this index number, for example: to display the distance from the sun.
 |
| The input file. |
 |
| The output of the program. |
REM demonstrates
REM (a) setting up a record structure
REM (b) reading from a file
REM (c) performing a linear search
INSTALL @lib$+"stringlib" : REM used by FN_removeCRLF()
file$ = @dir$+"planetsInput.txt"
NumRecords% = FN_countRecordsInFile( file$ )
REM now we know how many records there are
REM we can set up a record structure
DIM Planet{(NumRecords%-1) name$, distance }
PROC_readDataIn( file$, Planet{()}, NumRecords% )
REM main loop
REPEAT
INPUT "Enter planet name : " myplanet$
index% = FN_search( Planet{()}, NumRecords%, myplanet$ )
IF index%<>-999 THEN
PRINT "Planet "Planet{(index%)}.name$
PRINT "Distance from sun : " STR$( Planet{(index%)}.distance/1000 )" thousand km"
PRINT "---------------------------------------------------"''
ELSE
PRINT "No record found"''
ENDIF
UNTIL FALSE
STOP
DEFFN_countRecordsInFile( filepath$ )
REM opens a file for reading and counts the number of records in the file
LOCAL file%
LOCAL mycount%
LOCAL dummy$
file% = OPENIN( filepath$ )
WHILE (NOT(EOF#file%))
REM I know that each record has two fields
INPUT#file%, dummy$, dummy$
mycount% += 1 : REM count one record
ENDWHILE
REM REMEMBER to close the file once we are done
CLOSE#file%
= mycount%
DEFPROC_readDataIn( filepath$, this{()}, n%)
REM reads data from the file into a the data structure
LOCAL i%
LOCAL file%
LOCAL name$, distance$
file% = OPENIN( filepath$ )
FOR i% = 0 TO n% -1
INPUT#file%, name$, distance$
REM remove the Carriage returns/Linefeeds
REM and store in the structure
this{(i%)}.name$ = FN_removeCRLF(name$)
this{(i%)}.distance = VAL( FN_removeCRLF(distance$))
NEXT
REM REMEMBER to close the file once we are done
CLOSE#file%
ENDPROC
DEFFN_search( this{()}, n%, key$ )
REM performs a linear search for the key in the
REM array of records
LOCAL found%
LOCAL i%
LOCAL a% : a% = -999 : REM assume record wont be found
WHILE NOT(found%) AND i% < n%
REM is the current record the one with matching key?
IF this{(i%)}.name$ = key$ THEN
REM yes, then found it!
found% = TRUE
a% = i% : REM return the index for the found record
ELSE
REM no
i% += 1 : REM look for the next one
ENDIF
ENDWHILE
= a%
DEFFN_removeCRLF(t$)
REM returns the text passed with carriage returns and line feeds removed
LOCAL dummy%
dummy% = FN_findreplace(t$,CHR$(13),"",0)
dummy% = FN_findreplace(t$,CHR$(10),"",0)
= t$
#linearSearch
#algorithms
#computing