E0001 Computers in Engineering

E0001 Computers in Engineering DO .... LOOP

Readings • Schneider Chapter 6 sections 6.1 and 6.2 - problems as required • Schneider p 84 on This Lecture: • two types PRETEST DO.. LOOPS

Assignment Documentation • Flowcharts OR pseudocode for main routine and ALL subs and functions • overviews for main, subs and functions • written paragraph/s stating what it does, how it does it, variables used from and returned to main routine • code with comments • screen dumps - ask in tut • write protected disk with code • flowcharts etc printed one staple in corner in folder

DO LOOP • loops repeat a set of statements - used when an UNKNOWN number if iterations is required • DO indicates the top of the loop LOOP indicates the end of the loop • DO without a LOOP and visa versa will give a run time error. Same rules for NESTED loops apply • four ways to write a DO LOOP • pre & post test; WHILE & UNTIL

Pre - test Loop condition tested before statements are executed DO WHILE condition statement (s) LOOP • statements executed if condition true DO UNTIL condition statement(s) LOOP • statements executed if condition false or UNTIL condition true

execute statements in loop true condition false Pretest WHILE loop flowchart DO WHILE condition loop statements LOOP

Pretest UNTIL loop flowchart execute statements in loop false condition true DO UNTIL condition loop statements LOOP

conditions • conditions use RELATIONAL and LOGIC operators • evaluated to TRUE or FALSE • if conditions are not met, the control passes to statement immediately after the LOOP • control value must be able to be changed in loop else infinite loop

sum =0 i=0 DO WHILE sum<1000 i = i+1 sum = sum +i LOOP PRINT “sum of first”;i ;”integers is”;sum ‘initalise sum to zero ‘as long as sum <1000 ‘set i to next integer and add to sum ‘repeat Example

sum =0 i=0 DO WHILE sum<1000 i = i+1 sum = sum +i LOOP PRINT “sum of first”;i ;”integers is”;sum sum =0 i=0 DO UNTIL ??????? i = i+1 sum = sum +i LOOP PRINT “sum of first”;i ;”integers is”;sum Write a corresponding DO UNTIL loop

sum =0 i=0 DO WHILE sum<1000 i = i+1 sum = sum +i LOOP PRINT “sum of first”;i ;”integers is”;sum sum =0 i=0 DO UNTIL sum>1000 i = i+1 sum = sum +i LOOP PRINT “sum of first”;i ;”integers is”;sum similar loop using UNTIL pretestequivalent condition

uses for DO LOOPS • to read or process an unknown number of data • used with ‘flags’ • re-run programs until user choice to finish

examples DO WHILE choice$<>“n” sum =0 i=0 DO WHILE sum<1000 i = i+1 sum = sum +i LOOP PRINT “sum of first”;i ;”integers is”;sum INPUT “continue?y/n”; choice$ LOOP original program nested loop

using flags (flag = 1) DO LOOP WHILE flag = 1 flag = 0 FOR i = 1 TO 19 bar(i) = (bar(i - 1) + bar(i) + bar(i + 1)) / 3 actualtoler = ABS(oldbar(i) - bar(i)) IF actualtoler >= tol THEN flag = 1 PRINT i, bar(i), oldbar(i), actualtoler oldbar(i) = bar(i) NEXT LOOP

process data; used with files and eof or eod markers eod - end of data marker in this case 999 sum =0: n=0 READ v DO WHILE v <> 999 sum = sum +v n = n+1 READ v LOOP average = sum/n DATA 21,22,23,25,4,55,67,999

eod with string data and multiple reads READ name$, address$, age DO WHILE name$ <> “eod” PRINT name$, address$,age total = total +age n = n+1 READ name$, address$, age LOOP PRINT “average age”;total/n DATA harry, 10 smith, 24, eod, 0, 0

E0001 Computers in Engineering