README.md

Computer Programming (in C) Monsoon 2022

Lec 20: Recursion I

Factorial | Fibonacci | n choose k
Slides | factorial.c | fib.c | choose.c
Read:

• https://redirect.cs.umbc.edu/~chang/cs202.f98/readings/recursion.html
• Section 7.3 in https://hal.inria.fr/hal-02383654/file/ModernC.pdf
• https://web.mit.edu/6.005/www/fa15/classes/10-recursion/

Solve:

• Write a program which prints all permutations of numbers from $n$ to $n+k-1$. Input is $n,k$. (see slides last page).
• Write a program which takes input a number $n$, and an $n\times n$ matrix and outputs the determinant of that matrix.

Lec 21: Recursion II

Euclids GCD | Fibonacci using Cache | Determinant | Typedef | Enumerating Permutations
slides | fib_cache.c | det.c | perm.c
Read:

• https://en.wikipedia.org/wiki/Recursion_(computer_science)

Solve:

• Write a recursve program to find the shortest path from $(1,1)$ to $(n,n)$ in an $n\times n$ grid with obstacles. (see slides for some ideas).
• Write a program for enumerating all $k$ element subsets of an arbitrary $n$ sized set. Algorithm should work on $n = 20, k=10$ reasonably fast.
  - Input: $k, n,$ and $S$ (an arbitary set of $n$ numbers)
  - Output: Print every subset of $S$ of size $k$.
  - Example: On input 2, 4 and 1 2 3 4, ouput 1 2, 2 3, 3 4, 1 3, 1 4, 2 4. Explore:
• https://natureofcode.com/book/chapter-8-fractals/
• http://recursivedrawing.com/

Lec 22: Recursion III

GDB | Recrusive Drawing
Recursive Drawing using Skia Fiddle (on web) | Recursive Drawing using Allegro code
Read/Watch:

• GDB Commandline debugging: https://www.youtube.com/watch?v=svG6OPyKsrw
• VSCode debugging: https://www.youtube.com/watch?v=SkhHzpXw8F8
• Visualizing Algo: https://visualgo.net/en/recursion

Solve:

• Draw a tree using recursive drawing Or even better (can be done in 10 lines of code):

Solution in Skia (web). Skia Drawing Examples: 1 2 3

Lec 23: Recursion IV - Mergesort

Mergesort | More GDB | Passing Pointers
slides | sort.c
Read:

• Call by Value/Reference: https://www.scaler.com/topics/c/call-by-value-and-call-by-reference-in-c/
• Passing Multidim array to func: https://solarianprogrammer.com/2019/03/27/c-programming-passing-multi-dimensional-array-to-function/
  Note that we have been using the last method in the above writeup.
• MergeSort: https://www.ics.uci.edu/~goodrich/teach/cs260P/notes/MergeSort.pdf

Solve:

• Write a recursing program which given an array and a number, returns the position of the number in the array. If the number is not present, returns -1.
• A 2D array M is said to be sorted, if every row and every column of M is sorted. Given an input 2D array, write an progam to sort it.

Lec 24:Abstract Data Type I

struct | struct from struct | array of struct | pointer to struct
slides | point.c | draw circles with struct | draw tree with struct
Read:

• https://codeforwin.org/2018/06/structures-in-c-programming-need-and-use.html
• https://beginnersbook.com/2014/01/c-structures-examples/
• Go through the examples: https://github.com/gowthamrajk/Structure-and-Pointers-in-C/tree/main/Structure%20in%20C
• https://www.tutorialspoint.com/cprogramming/c_structures.htm

Solve:

• See the comments in the file for the problem statement: social_nets.c (3 problems are mentioned).

Lec 25: Abstract Data Type II

Example application of using Structs to build a Reciept/Customer Management System
slides | srms.c
Read:

• Strings in C
  https://www.programiz.com/c-programming/c-strings | https://www.programiz.com/c-programming/string-handling-functions
• Getting current date time in C
  https://www.tutorialspoint.com/c_standard_library/c_function_localtime.htm

Solve:

• Modify srms.c to include an option 2 for listing all reciepts for a particular customer. On entering option 2, the program should ask for a phone number and then slow the list of reciepts sorted chronologically.
• Modify srms.c to include option 3 giving the total revenue on a particular day. On entering option 3, the program should ask for a day and print out all the reciepts issued on that day followed by the total revenue.

Doubt Clearing with Instructor Session I : Pointers and Recursion

perm.c

Lec 26: Abstract Data Type III

Enums | Strings in C | Social Network application
slides | enum.c | str.c | social_net.c

Solve:

• Find mutual friends in social_nets.c
• Given 2 names, check if they connected through their friends.
  • Input: 2 strings name1, name2
  • Output: check if there is a person p such that p is a friend of name1 and name2 is a friend of p.

See respective folders under lecs for material for remaining lectures.