Adding Up a List of Numbers

Here is a program that adds up each integer from START to FINISH.

' Add up the integers from START to FINISH
'
LET TOTAL = 0    ' TOTAL will hold the sum
LET START = 1
LET FINISH = 5
'
FOR COUNT = START TO FINISH
  LET TOTAL = TOTAL + COUNT
  PRINT COUNT, "has just been added to TOTAL which is now", TOTAL
NEXT COUNT
'
PRINT "The total is:", TOTAL
END

TOTAL starts out at zero. Each time the loop is executed, COUNT will be added to TOTAL. COUNT will start out at 1 and will finish at 5. The program will print out:

1 has just been added to TOTAL which is now 1
2 has just been added to TOTAL which is now 3
3 has just been added to TOTAL which is now 6
4 has just been added to TOTAL which is now 10
5 has just been added to TOTAL which is now 15
The total is:  15

If this is not clear, follow through the program line by line (or type it into QBasic and use the debugger.) The line

LET TOTAL = TOTAL + COUNT

is done in two steps: the right-hand side adds COUNT to what is in TOTAL, then that result is put back in TOTAL.