# Little Man Computer: Multiplication

Write an LMC program to let the user enter two numbers, num1 and num2.
The program should output the results of multiplying these two numbers: num1 x num2.

#### Solution

While checking the Little Man Computer Instruction Set (See table at the bottom of this post), you will have noticed that, through there are two instructions for adding (ADD) and subtracting (SUB) numbers, there is no instruction for multiplying two numbers.

The solution to overcome this, is two consider a multiplication as a series of additions. For instance:

5 * 4 = 5 + 5 + 5 + 5

This is how we will implement our multiplication algorithm:

```        INP
STA NUM1
INP
STA NUM2
LOOP    LDA TOTAL
STA TOTAL
LDA NUM2
SUB ONE
STA NUM2
BRP LOOP
LDA TOTAL
SUB NUM1
STA TOTAL
OUT
HLT
NUM1    DAT
NUM2    DAT
ONE     DAT 1
TOTAL   DAT 0```

#### LMC Instruction Set

Note that in the following table “xx” refers to a memory address (aka mailbox) in the RAM. The online LMC simulator has 100 different mailboxes in the RAM ranging from 00 to 99.

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