(11C) Finding biggest of 3 integers

[Dieter]

(10-20-2018 05:41 AM)Gamo Wrote:  Program to find the biggest number of 3 integers.

Of any three numbers, not only integers.

Gamo, do you remember the following sequence?

With two numbers in X and Y, X≤Y? X<>Y checks if X is the smaller of the two. If it is, both are swapped.
So this sequence always returns the larger number in X and the smaller one in Y.

Likewise, X>Y? X<>Y returns the smaller number in X and the larger one in Y.

Now assume there are three different numbers in X, Y and Z.
X>Y? X<>Y will put the larger one in Y and the smaller one in X.

Roll down the stack one level to compare this larger number with the third one.
X≤Y? X<>Y will put the largest of all three in X.

So the program simply is:

Code:

01 LBL A
02 X>Y?
03 X<>Y
04 R↓
05 X≤Y?
06 X<>Y
07 RTN

Or on the 12C and others without an X>Y? test:

Code:

01 X≤Y?
02 X<>Y
03 X<>Y
04 R↓
05 X≤Y?
06 X<>Y
07 GTO 00

You can easily extend this example. This is what we get:

Return the largest of two numbers:

Code:

01 LBL A
02 X≤Y? 
03 X<>Y
04 RTN

Return the largest of three numbers:

Code:

01 LBL A
02 X>Y?
03 X<>Y
04 R↓
05 X≤Y?
06 X<>Y
07 RTN

Return the largest of four number:

Code:

01 LBL A
02 X>Y?
03 X<>Y
04 R↓
05 X>Y?
06 X<>Y
07 R↓
08 X≤Y?
09 X<>Y
10 RTN

Dieter