CODEWITHSUNDEEP
assemblymarie
BradBeighton
BradBeighton

Reputation: 93

How to determine whether two numbers are equal

I am on the following task in MARIE (Machine Simulator Environment):

Allow the user to input 2 numbers.

Compare them.

If the two numbers are the same: output a 1

If they aren't the same: output a 0.

So far I've got the bare minimum:

INPUT 
STORE X 
INPUT 
STORE Y 
HALT 

X, DEC 010 
Y, DEC 011

But I don't know what to do next. Which are the instructions to use for comparing the inputs for equality, and to output a different output (0 or 1) depending on that comparison?

Upvotes: 3

Views: 3598

Answers (2)

trincot
trincot

Reputation: 350242

To compare numbers in MARIE for equality, you subtract them. After the subtraction you then check whether the result is 0, using SkipCond 400.

You only need to store one of the inputs, as you can immediately subtract the first input from the second, without actually storing the second input.

To output 1 when the inputs are equal, and 0 otherwise, you can have two code blocks, one that loads the value of 0 and outputs it, and another that loads the value of 1 and outputs it, and then execute the one of these two blocks that is relevant. This is the approach taken in the answer of user3956566.

But you could also do this (in pseudo code):

Input X
Input Y
acc := X - Y
If acc != 0 Then 
    acc := -1
End If
acc := acc + 1
Output acc

After the if has executed, you know that acc will be either -1 or 0. Then it is easy to adapt that to 0 or 1 respectively.

In MARIE:

Input 
Store X
Input
Subt X
SkipCond 400    / If difference is non-zero ...
         Load MinusOne  / ... then load -1
Subt MinusOne   / In either case: add 1
Output
Halt

X, Dec 0
MinusOne, Dec -1

This is a rare case when you don't put a Jump instruction right after a SkipCond instruction.

Upvotes: 0

user3956566
user3956566

Reputation:

Have one variable to store input. Then subtract the next input from it. If the result is zero skip to print a 0. Otherwise print a 1 and then jump to the end of the program

    Input
    Store Num

    Input
    Subt Num
    Skipcond 400 
    Jump Equal  /If zero the numbers are equal

    Load One
    Output
    Jump End

Equal, Load Zero
    Output
End, Halt

/ declarations
Num, Dec 0
Zero, Dec 0
One, Dec 1

Upvotes: 1

Related Questions