Post-class 01/24

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 ```
 
 - This is the same idea as passing variables as copies versus as pointers to memory
+
+---
+
+[-> Notes 01/24](01-24.md)
diff --git a/01-24.md b/01-24.md
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+[\<- Notes 01/17](01-17.md)
+
+---
+
+# Unions
+
+- A union is a data structure that overlays components in memory
+	- Allows one chunk of memory to be interpreted in multiple ways
+- The union is used for saving space
+	- In situations in which one needs a data object that can be interpreted in a variety of ways
+
+Declaration Outline:
+
+```
+union union_t{
+	variable declaration;
+	variable declaration;
+	...
+};
+```
+
+Alternatively, you can use `typedef`:
+
+```
+typedef union{
+	variable declaration;
+	variable declaration;
+	...
+} UNION_T;
+```
+
+Both examples above are type definitions and do not allocate memory
+
+Union Example:
+
+```
+typedef union{
+	int age;
+	char artist[20];
+} ART_INFO;
+```
+
+- Defines a Union Type
+	- The name of `ART_INFO` is the union tag
+	- The identifiers are called members (like in structures)
+	- Members can be any valid C data type
+	- With this example, `ART_INFO` can be used like int, char, etc.
+
+```
+ART_INFO info;
+```
+
+- `info` is a variable
+- `info` **does not have both components**
+	- Amount of memory allocated depends on the largest component in the union
+- the member variables are accessed using the dot operator
+
+```
+info.age = 2000;
+```
+
+or
+
+```
+strcpy(info.artist, "Michelangelo");
+```
+
+- Member names are local and not known outside the union
+
+- Like structures, unions can be declared as an array of unions:
+
+```
+ART_INFO info_array[20];
+
+info_array[0].age = 1000;
+```
+
+- Pointers to unions can be declared
+	- Like with structures, arrow operator is used to access members for pointers
+
+- Union example in a Structure:
+
+```
+typedef union{
+	int age;
+	char artist[20];
+} ART_INFO;
+
+typedef struct{
+	char name[20];
+	int class;
+	ART_INFO info;
+} ART_CLASS;
+
+ART_CLASS class_array[4] = 
+{{"Mask of Agamemnon", 0, .info.age = 3500},
+{"Mona Lisa", 1, .info.artist = "Leonardo da Vinci"},
+{"Nok rider and horse", 0, .info.age = 2000},
+{"Pieta", 1, .info.artist = "Michelangelo"}};
+```
+
+- Be careful not to reference an invalid member in your union!