CS 115 Lab 6 A Random Robot Walk

75 Points

Due Date: Monday March 15, at end of lab

Educational goals of this lab - verify that every student can

understand and write if statements
understand while loops
use an accumulator
get a random number

Use the Canvas link to submit your work.

You May NOT use break or any of the statements that break the guarantees of structured programming (pass, continue, exit). This will cost you ALL points of the assignment if you do. It is perfectly possible to follow the design given and not need these!

INSTRUCTIONS:

(75 points) Description of the Problem:

There is a concept called "The Drunkard's Walk" or a "random walk". The idea is that some things in life are not predictable but follow a random path. In mathematical terms, it is a path that consists of a succession of random steps. For example, the path traced by a molecule as it travels through a liquid or a gas, the search path of a foraging animal, the price of a stock, the financial status of a gambler. ref
Your program is going to simulate this using random numbers. This walk is only going to be in one dimension.
Imagine a bridge that is 10 "steps" wide. A robot is trying to cross the bridge. Unfortunately it has a defect which causes it not to be able to go straight forward but only steps to one side or the other.
The program's job is to ask the user how many steps they want to run the simulation, then display the outcome. The simulation ends either by finishing the number of steps the user requested, or by falling off the bridge on either side.
Sample: (does not fall off)
```
Random Robot Walk

How many steps to take? 10
|1234567890|
|     R    |
|      R   |
|       R  |
|      R   |
|       R  |
|      R   |
|       R  |
|        R |
|       R  |
|        R |
|         R|
it did not fall off the bridge!
Robot took 10 steps
```
Note that the robot starts at the middle of the bridge, that's why there are eleven R's printed. The position of the robot at the start is printed on the first line.
Another Sample: (falls off the right edge)
```
Random Robot Walk

How many steps to take? 300
|1234567890|
|     R    |
|    R     |
|     R    |
|      R   |
|       R  |
|        R |
|         R|
|        R |
|         R|
Splash!
Robot took 9 steps
```
The ninth step is not shown, that's what made it fall off the bridge.
Sample run: (falls off the left edge)
```
Random Robot Walk

How many steps to take? 50
|1234567890|
|     R    |
|      R   |
|     R    |
|      R   |
|     R    |
|    R     |
|   R      |
|  R       |
| R        |
|  R       |
| R        |
|  R       |
|   R      |
|  R       |
| R        |
|R         |
| R        |
|R         |
Splash!
Robot took 18 steps
```

(10 points) Problem #1: Complete a test plan.

It is harder to test a program using random numbers.
The answers will not be definite paths, you don't know what the random directions
Put the answers as comments at the end of the program file.
Do these FIRST before your program is written!
You can assume the header "1234567890" will be displayed every time, so it isn't necessary to note it in the results.
It is assumed this is based on a bridge 10 steps wide.

Description	Input (number of steps)	Expected behavior/output
Zero iterations	0	Starting position shown, did not fall off, Robot took 0 steps
One iteration	1	_____A._____
More than one iteration, less than 5	4	_____B._____
Five or more iterations	10	_____C._____

(12 points) Problem #2: Design

Copy and paste this design into a python file. Fill in the blanks in the design so that it solves the problem and shows the control structures (loop and ifs) and what they are supposed to do.

# Prolog including 3 P's and author's name 

# import _________________ library

# print title
# initialize the width of the bridge  (set to 10 to start with, you can change it later)
   #and the counter for steps to zero
   #and the robot's location to center of bridge (calculate it!)

# ask user ____________________
# print the header
# while counter has not done that many steps and robot's location > 0 and ______________

   # print the robot's location on bridge
   # get a random direction to take on next step (either -1 or 1)
   # add direction to robot's location
   # add one to _____________

# if didn't fall off bridge
   # print last step of robot, tell user
# else
   # print __________

# report _______________________

(53 points) Problem #3: Complete the program.

Implement the program starting with the .py file you have written the design in. The design steps are the comments.
You will need to use the replication operator (*) to align the Robot symbol. Think of how many spaces you need to the left of the Robot, how many spaces to the right you need.
Example to help understand - try this little program!
```
def main():
    for z in range(1, 10):
        print(" " * z, ":)")
main()
```
A piece of code you can use
```
    #if robot is in position x and the bridge is width positions wide
    print("|", " " * x , "R", " " * (width - x) , "|", sep="")
```
Use a random library function to choose the direction change. An integer value is easiest here, so you can just add it to the robot's location. Use -1 to go to the left, 1 to go to the right. How can you call a function that will give you just those two numbers?
Think about how you control the while loop. There are THREE conditions! The robot could fall off the bridge on the left side or on the right side.
Instead of hardcoding in the number 10 as the width of the bridge, assign the 10 to a variable and use that through the whole program. That way, when you want to try a wider bridge, you can easily do it by changing one variable's value.
Notice that the Robot's last step is printed ONLY if it does not fall off the bridge.
Use the Minimum number of if's, comparisons, possible. Make sure your branches contain ONLY the code that is needed. If you see repeated code in each branch, take it OUT and do it ONE time!
Submit your finished program with the Canvas link.