QuickBasic Cafe Forum

Hello everyone,

   I am trying to write QBasic code to find the variance of the following situation.  I am a newbie when it comes to QBasic.  Any help received would be appreciated.  Thank you in advance.  You may also send replies to mikecurl74@aol.com.

***Find the mean (M), the variance (V), and the Highest Number entered of a variable number of student grades (n).  The formulas for the mean and variance are as follows:

M= (G1+G2+G3)/n
(I have this working.)

V= [(G1-M)2+(g2-m)2+...(Gn-M)2]/(n-1)

( I can't get that to come out right.  Any suggestions?  Or is the code completely wrong for the variance?  Is there a way to write the variance formula so that it makes since in QBasic?)

Mike
mikecurl74@aol.com

You might want to try declaring you variable out front.
Intergers will only goto 32767. Try using
DIM G as single
DIM M as single
etc.
if not try
DIM G as DOUBLE
etc.
You must leave enough room for large numbers

good luck

Try this:

DEFDBL A-Z
CLS

M = 0: V = 0
n = 3

DIM G(1 TO n)
DATA 7,8,34

FOR i = 1 TO n
READ G(i)
NEXT i

'M = (G1+G2+G3)/n
FOR i = 1 TO n
M = M + G(i)
NEXT i
M = M / n

'V = [(G1-M)2+(g2-m)2+...(Gn-M)2]/(n-1)
FOR i = 1 TO n
V = V + (G(i) - M) * 2
NEXT i
V = V / (n - 1)

PRINT "M ="; M
PRINT "V ="; V

Thanks for the help guys.  It does work that way.  But what if I don't know how many grades will be entered?  Is there a way I can set it up to use an unknown variable instead of entering the grades themselves in the program?

Mike

Well, you need to use a loop like

DO
INPUT "GRADE" G(i)
i = i + 1
LOOP


instead of READ G(i)

also, you need to output what the sentinel, or terminating input is

ie:
LIMIT = 100   ' max number of grades to be entered
DIM g(LIMIT - 1)

print "ENTER "101" to end.
i = 0
DO
INPUT "GRADE", grade

if grade >= 0 and grade <= 100 then
G(i) = grade
&nbsp;i = i + 1
end if

LOOP UNTIL grade = 101 or i = LIMIT


there must be some limit, the limit i think is 32767 for array spaces, but thats probly more than you need, just be sure to DIM the array of grades high enough

This is the complete code including Frankybaby's input routine:

DEFDBL A-Z
CLS

M = 0: V = 0
LIMIT = 100   ' max number of grades to be entered
MAXGRADE = 100
DIM G(1 TO LIMIT)

PRINT "ENTER "; MAXGRADE + 1; " to end. "
n = 0
DO
   PRINT n + 1;
   INPUT ". GRADE: ", grade
   
   IF grade >= 0 AND grade <= MAXGRADE THEN
    n = n + 1
    G(n) = grade
   END IF
LOOP UNTIL grade = MAXGRADE + 1 OR n = LIMIT
IF n < 2 THEN END

'M = (G1+G2+G3)/n
FOR i = 1 TO n
M = M + G(i)
NEXT i
M = M / n

'V = [(G1-M)2+(g2-m)2+...(Gn-M)2]/(n-1)
FOR i = 1 TO n
V = V + (G(i) - M) * 2
NEXT i
V = V / (n - 1)

PRINT
PRINT "M ="; M
PRINT "V ="; V