### Over and over ... A loop is part of a program that gets repeated a number of times. The very first Pascal program you did had a loop in it. Loops can be conditional in which case they repeat until something happens - a condition is met - or they can be unconditional, in which case they are repeated for a fixed number of times. You've already seen an example of an unconditional loop - look back at the first program in this tutorial. The loop starts with... FOR index := 1 TO 10 DO ... and the instruction(s) to be repeated go between a BEGIN and an END statement: BEGIN WRITELN(index) END In this case the variable called index is a counter which controls the loop - it starts at 1 and goes up to 10 #### i) Unconditional Loops Recall Example 6 where a teacher wanted to read in three marks and calculate the average. Now consider what would happen if there were 10 or 20 or 200 marks... ...well this is what loops are designed for and if we know in advance how many times the loop is to be repeated, then so much the better! Here's a different design for the program. As each mark is read in, we're going to keep a running total: 1. get information from user 2. calculate average 3. print results Step 1 becomes: 1.1 set total to zero 1.2 loop for each student 1.3 prompt user to enter mark 1.4 read in the mark 1.5 update the total 1.6 end loop Step 2 is: 2.1 average = total / number of marks Step 3 is: 3.1 print out the total marks 3.2 print out the average mark So the complete design looks like this:

1.1 set total to zero 1.2 loop for each student 1.3 prompt user to enter mark 1.4 read in the mark 1.5 update the total 1.6 end loop 2.1 average = total / number of marks 3.1 print out the total marks 3.2 print out the average mark

type in this program and save it as average2.pas

PROGRAM unconditional; VAR mark : INTEGER; total : INTEGER; BEGIN total := 0; FOR counter = 1 TO 10 DO BEGIN WRITE ('type in the exam mark: '); READLN (mark); total := total + mark END; average := total / 10; WRITELN('the total is: '); WRITELN('the average is: ', average) END.

there are two mistakes in the program which means that it won't compile until you find them - can you see what they are? there are two more mistakes that you should be able to find when you run the program - can you fix them? Here's a better design that lets the user decide how many students there are:

1.1 set total to zero 1.2 prompt user to enter number of students 1.3 read in number of students 1.4 loop for each student 1.5 prompt user to enter mark 1.6 read in the mark 1.7 update the total 1.8 end loop 2.1 average = total / number of students 3.1 print out the total marks 3.2 print out the average mark

can you make the necessary changes to your program? See your teacher if you're not sure how to do this. Notice in this example what is meant by a 'running total' and notice also the line in the program that updates this total.
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