From c25938a3064b1cc73af26ea8db297a55f26949bf Mon Sep 17 00:00:00 2001
From: loshprung <lshprung@scu.edu>
Date: Fri, 14 Feb 2020 11:33:49 -0800
Subject: Post-class 02/14

---
 02-12.md |   4 +++
 02-14.md | 120 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 124 insertions(+)
 create mode 100644 02-14.md

diff --git a/02-12.md b/02-12.md
index ce40fa9..6e5dd1f 100644
--- a/02-12.md
+++ b/02-12.md
@@ -154,3 +154,7 @@ void compare(FILE *fp1, FILE *fp2){
 	return;
 }
 ```
+
+---
+
+[-> Notes 02/14](02-14.md)
diff --git a/02-14.md b/02-14.md
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--- /dev/null
+++ b/02-14.md
@@ -0,0 +1,120 @@
+[\<- Notes 02/12](02-12.md)
+
+---
+
+# Arguments for main()
+
+To add arguments to main, do something like this:
+
+```
+int main(int argc, char *argv[])
+```
+
+- `int argc` is the number of arguments
+	- the name (`a.out`) is an argument, so there will always be at least one argument
+- `char *argv[]` is an array of strings, where each is an argument for the program
+- example, if you want two arguments, check that argc is the correct value: `argc == 3` (since you need one for the execution)
+
+# Recursion (not on Midterm #2)
+
+- A recursive function calls itself or is part of a cycle in the sequence of function calls
+	- Allows for the possibility for a function call to be repeated with different parameters
+
+- Alternative to iteration
+	- less efficient
+	- more simple
+
+- You will never use a loop ina recursive function
+	- recursion is meant to substitute the use of loops
+
+- Problems that lend themselves to a Recursive Solution:
+	- simple cases with a a straightforward solution
+	- cases can be redefined to be simplified
+	- redefinition process can reduce complex problems to simple cases (relatively easy to solve)
+
+General form:
+
+```
+if this is a **simple case**
+	solve it
+else
+	**redefine** the problem using recursion
+```
+
+Example: we want to multiply 6 by 3, but we only know how to add, and that x \* 1 = x
+
+```
+int multiply(int m, int n){
+	int ans;
+
+	if(n == 1) ans = m;
+	else ans = m + multiply(m, n-1);
+	return(ans);
+}
+```
+
+- Recursion can be useful for processing varying-length lists
+	- Strings
+	- Linked-lists
+	- Etc.
+
+Example: write a function to count the number of times a particular character appears in a string
+
+```
+int count(char ch, char *str){
+
+	if(*str == '\0') return 0;
+	if(ch == *str) return(1 + count(ch, str+1));
+	else return(count(ch, str+1));
+
+}
+```
+
+## Traversing Recursive Functions
+
+- *Hand Tracing* can be used to better understand how recursion works
+	- going through function calls step-by-step
+
+- Parameters and Local Variable Stacks
+	- Local function values are kept in a *stack*
+	- A *stack* is a data structure
+		- last data item in is first data item out
+	- *system stack* is an area in memory where parameters and local variables are
+		- allocated when a function is called
+		- deallocated (freed) when the function returns
+	- When a program is executing:
+		- Calling a function "pushes" its local values onto the top of the stack
+		- Returning from a function "pops" its local values from the top of the stack
+
+## Math Function and Recursion
+
+- Many mathematical functions are defined recursively
+
+- Example: Factorial
+	- 0! = 1
+	- n! = n \* (n-1)! for n>0
+- As a function:
+
+```
+int factorial(int n){
+	int ans;
+
+	if(n == 0) ans = 1;
+	else ans = n * factorial(n-1);
+
+	return(ans);
+}
+```
+
+- Example: The Fibonacci Sequence ([Spiral Out](https://www.youtube.com/watch?v=Y7JG63IuaWs))
+
+```
+int fibonacci(int n){
+	int ans;
+
+	if(n == 0 || n == 1) ans = n;
+	else ans = fibonacci(n-1) + fibonacci(n-2);
+
+	return ans;
+}
+```
-- 
cgit