Day 3

day3/README.md

@@ -0,0 +1,90 @@
+# Day 3
+
+## Functions
+
+Mathematically speaking, functions are able to take in a set of inputs and
+return a specific output. C++ gives you an interface by which you can create
+your own custom functions for purposes of modularity or recursion (where
+functions are necessary).
+
+The general structure of a function is as follows:
+
+```cpp
+(type that the function returns) (function name) (parameters) {
+  // body
+}
+```
+
+We will now more closely analyze each of the parts of this function.
+
+### Parameters
+
+The parameters that you put into your function are a template for how the
+function will work when it is actually called.
+
+The format of the parameters must be `(type) (name)`, with the parameters
+separated by commas.
+
+For instance, if you had a function to add two numbers, it would look something
+like this:
+
+```cpp
+int add (int a, int b) {
+  return a+b;
+}
+```
+
+Note that the variables `a` and `b` are simply aliases that you use to represent
+the actual values that you place into the function when you make a call.
+
+When you make the following function call,
+
+```cpp
+cout << add(3, 2);
+```
+
+`a` will represent 3 and `b` will represent 2, and thus this code block will
+print `5`. However, note that we cannot make the following call, as the
+arguments are not in the types that the compiler expects them to be in:
+
+```cpp
+cout << add(3, "string");
+```
+
+The function expects two integers, but received a string, which cannot be
+automatically converted to an integer for very obvious reasons.
+
+Note that c++ will conduct automatic type conversion whenever possible to allow
+the function to execute, so you can pass in a `long long` or `bool` and the
+function should still be able to convert them into `int`s.
+
+### Type
+
+Sometimes, you want your functions to return back a value for your convenience.
+For instance, if you have a simple function to add two numbers, you would want
+to get the sum of the numbers back. In this case, you place the return type at
+the front of the function signature as shown above
+
+Note that if you do wish to return a type in your function, you **must** return
+the value of that type in **all possible cases**, or else your compiler will
+throw a warning.
+
+The `void` keyword is special, as it is used for a function that does not return
+any value and only has side effects.
+
+For instance, if I were doing a floodfill traversal of a graph (where we are
+simply trying to find the number of disjoint regions), I would probably do the
+following:
+
+```cpp
+void dfs(int x, int y) {
+  // mark as visited
+  // propagate
+}
+```
+
+Note that the DFS does not actually return any real value, we simply use it for
+the fact that it is able to fill out the visited array.
+
+When you use a function that returns `void`, you will not actually have to
+provide an explicit `return` statement.

lab/Main.cpp

@@ -3,4 +3,5 @@ using namespace std;
 
 int main() {
     ios_base::sync_with_stdio(0); cin.tie(0);
+
 }