# 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:

#### 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.

 Mnemonic Name Description Op Code INP INPUT Retrieve user input and stores it in the accumulator. 901 OUT OUTPUT Output the value stored in the accumulator. 902 LDA LOAD Load the Accumulator with the contents of the memory address given. 5xx STA STORE Store the value in the Accumulator in the memory address given. 3xx ADD ADD Add the contents of the memory address to the Accumulator 1xx SUB SUBTRACT Subtract the contents of the memory address from the Accumulator 2xx BRP BRANCH IF POSITIVE Branch/Jump to the address given if the Accumulator is zero or positive. 8xx BRZ BRANCH IF ZERO Branch/Jump to the address given if the Accumulator is zero. 7xx BRA BRANCH ALWAYS Branch/Jump to the address given. 6xx HLT HALT Stop the code 000 DAT DATA LOCATION Used to associate a label to a free memory address. An optional value can also be used to be stored at the memory address.
Tagged with: ,