1. Little Man Computer
(continued)

2. All Instructions 1XX – add the value in mailbox XX to calc
2XX – subtract the value in mailbox xx from calc
3XX – put the value of calc into mailbox XX
5XX – take the value of mailbox XX and put it into calc
6XX – set the instruction counter to XX
7XX – set the instruction counter to XX if calc is 0, otherwise nap
8XX – set the instruction counter to XX if calc is positive, otherwise nap
901 – grab the top item from input and put it in calc
902 – put calc into output
000 – stop and go home

3. Conditional Execution
What if we want the our mail man to skip instructions?
For example, let’s say that you are an acturary
You need to write a program to calculate how many years an individual has left to live
You decide to offload this task to the mail man
The formula you decide to use is 80 - <input>
What happens if the user says they are -5 years old?

4. Conditional Execution
If the user enters a negative value, we want to output -1 instead of <input>

5. Conditional Execution Example
0 – 901 – read a # from the input and put it in calc 1 – 209 – subtract the # in mailbox 9 from calc 2 – 706 – if calc is now 0, set the instruction counter to 10, otherwise rest 3 – 512 – copy the # mailbox 12 to calc 4 – 902 – write the value to calc to the output 5 – 0 – go home 6 – 511 – copy the # mailbox 11 to calc 7 – 902 – write the value to calc to the output 8 – 0 – go home 9 – 5 10 – 6 11 – 1 12 – -1

6. Looping
Sometimes, you need to keep doing a set of instructions until a value reaches 0
For example, remember to simulate multiplication using repeated addition, we stopped once the number we were multiplying by reached 0

7. Looping Example
0 – 901 – copy # from input to calc 1 – 399 – copy calc to mailbox 99 2 – 901 – copy # from input to calc 3 – 398 – copy calc to mailbox 98 4 – 598 – copy mailbox 98 to calc 5 – 712 – if calc is 0 go to XX 6 – 215 – calc – mailbox XX 7 – 398 – copy calc to mailbox 98
8 – 597 – copy mailbox 97 to calc 9 – 199 – calc + mailbox – 397 – copy calc to mailbox – 604 – go to 4 12 – 597 – copy mailbox 97 to calc 13 – 902 – copy from calc to out 14 –