# Loops && Booleans¶

Lab Assignment: Loops && Booleans

## Your Assignment¶

The assertion that every *even* number is the sum of two *prime* numbers is
called Goldbach’s conjecture.

You will write a program that asks the user for an integer number, then checks if the integer is even, and finally determines two prime numbers that sum to the user’s entered integer number.

An easy way to map out this though is to write out a table. If I am testing
Golbach’s conjecture for the input number of `36`

(an even, non-prime
number), we run through the possible combinations of numbers less than 36, and
prime, that when summed, will equal 36.

`num` |
`i` |
`j` |
---|---|---|

36 | 1 | 35 (`num` - `i` ) |

36 | 2 | 34 (`num` - `i` ) |

36 | 3 | 33 (`num` - `i` ) |

36 | 4 | 32 (`num` - `i` ) |

36 | 5 | 31 (`num` - `i` ) |

… | ||

36 | 35 | 1 (`num` - `i` ) |

### Assignment Requirements¶

Three functions are required:

`get_input()`

:This function takes no parameters, but will ask the user for an integer number. It will

`return`

a valid integer. You will use an indefinite loop and exception handling like we discussed in class. It is required to catch user input error and gracefully recover. Learn about the`continue`

keyword and how it works in a loop; it can be handy.

`is_prime(n)`

:This function will take an integer parameter

`n`

, and return`True`

if the number is prime, or return`False`

if it is not prime. You can use this pseudocode for primality testing to write this function.

`main()`

:This does the bulk of your program’s work for solving Goldbach’s conjecture. You will call

`get_input()`

and`is_prime(n)`

from`main()`

.Goldbach’s conjecture itself will be solved using an indefinite loop. Particularly a ‘post-test’ loop pattern. A

`for`

loopwill not be accepted as part of the solution.

### Output¶

A successful run:

```
This program tests the Goldbach's conjecture
Please enter an even integer larger than 2: 36
36 = 5 + 31
```

A run recovering from errors:

```
This program tests the Goldbach's conjecture
Please enter an even integer larger than 2: 7
Wrong input!
Please enter an even integer larger than 2: foo
Bad input!
Please enter an even integer larger than 2: 8
8 = 3 + 5
```

If by chance the number chosen is valid, but doesn’t hold for Goldbach’s conjecture, then print:

```
Goldbach's conjecture doesn't hold for [whatever the number is]
```

*(I’m not aware of a number for which this occurs, but handle this possible
case anyways.)*

## Submission Requirements¶

Your file is **required** to be named `lab_loops_booleans.py`

.

Please read and follow the Submission Requirements to avoid point deductions specified below.

## Grading¶

The following is the grading rubric for this lab to be used by the course graders. The lab is worth 100 points.

*Note:* There may be additional criteria for grading, this is just a summary of the major
rubric items.

Type | Description | Point Loss (Max) |
---|---|---|

[General] |
||

`SyntaxError` Exceptions |
A program that doesn’t even start due to syntax errors. | -30 |

Docstrings | Missing proper lab header (e.g. no name, lab section, etc) | -10 |

`main()` |
Your program should have `main()` as the first-called function |
-10 |

PEP 8 Style | Egregious problems with your code styling | -10 |

Incorrect Filename | Follow the submission instructions | -5 |

Commenting | Insufficient or excessive comments | -5 |

[Lab Specific] |
||

Functions | Three functions are required: `get_input()` , `is_prime(n)` , and `main` |
-10 each/missing |

Indefinite Loop | The code for `get_input()` and `main()` is to be written using a `while` loop, only |
-15 |

Logic | Boolean logic errors for `if` , and `while` conditions |
-5/each |

### Extra Credit¶

Extra credit work must be submitted in what would be your original submission file for the assignment. All extra credit code

mustbe clearly commented in order to receive any points.

+5 points

Modify your program to read in a series numbers from a text file,

orask the user for one number, depending on what the user wants. The file format is to be specified by you, anddocumentedin your code. Additionally, a sample file must be provided as part of this extra credit so it can be quickly tested.+5 points

allpossible combinations of prime numbers that solve the conjecture (commutative results aren’t required, e.g.`5+3`

and`3+5`

are the same combination in my view).