Mentoring Worksheet - C

Welcome to the second mentor session! This workshop will have some theory-based questions similar to the examples Jamie will show you in lectures, and some practical exercises.

To get a copy of this repo (so you can code your own solutions), clone this repo by running the following command:

git clone https://github.com/aidandagnall/mentoring21-22.git

Your mentor should be running this session with you, so feel free to ask any questions to them either during your meeting, or afterwards through Teams or Discord.

Theory Questions

Question 1

How would you declare each of the following datatypes in c? Use any variable name you like.

• An integer array of length 16.

• A 2D array of characters, 8x8 length.

• An integer pointer.

• An array of integer pointers of size 10.

• Question 2

void func1(int *n) {
    n = 10;
}

int func2(int *x, int *y) {
    *x += *y;
    return *x++;
}

int main() {
    int i, j, k = 20;

    /* A */

    j = ++k;
    i = j++;

    /* B */

    func1(&j);

    /* C */

    k = func2(&i, &j);

    /* D */
}

What are the values of a, b, and c at the following points in the code?

• A
• B
• C
• D

Practical Tasks

Task 1: Array Manipulation

Edit the multArrayBy function in task1.c.

It should multiply each value in the array from by n, then store the result at the same index in the array dest.

In: n = 2, from = {1, 2, 3}

Out: dest = {2, 4, 6}

Task 2: Fibonacci

Create a function to generate (and print) the fibonacci numbers up to n.

Write your implementation in the fib(int n) function, where n is the input value from the commandline (this is handled for you in main).

$ ./fibonacci 6
0 1 1 2 3 5

$ ./fibonacci 11
0 1 1 2 3 5 8 13 21 34 55

Extension Task: Generalise for any two starting numbers

Fibonnacci's sequence is part of a whole family of sequences called Lucas sequences, where the next number is given by adding the last two.

Generalise your function to the form int lucas(int a, int b, int n) where a and b are the starting values. Then, use this new function to generate another lucas sequence, the lucas numbers:

$ ./fibonnaci 2 1 8
2, 1, 3, 4, 7, 11, 18, 29

Task 3: Finding a sum in a data set (AOC 2020 Day 1)

Given an array of integers, find the two which sum (add) together to make 2020 .

Implement your solution in the solve function, where input is your array, and size is the array's length. Don't worry about reading in the numbers, we've done this for you. Just complete the solve function.

Your return value should be 926464.

Getting More Practice

The best thing you can do to improve your skills in C (and programming in general) is practice. These are some useful websites for you to try out if you want to go further.

If you enjoy these challenges, you may want to try some more. Sites like Project Euler is great for mathematical problems, but they get hard quickly. If you want to challenge yourself, try out the Advent Of Code this year. During Advent (1 - 25 Dec) there's a new programming problems every day, you can complete them in any programming language you want, and you can join the HackSoc leaderboard to compete with other people at the university! (Task 3 was from Advent of Code 2020!)

Sites like LeetCode or HackerRank are great for getting practice for interview questions when it comes to find a graduate job, year in industry placement or internship. challenges to help test your programming skills.

Try some of them out if you want to push yourself! Some of the mentors may be able to help with these if they've done them before too, so drop a message in #programming on the Discord server if you get stuck.