Add Day 16: Union, enum and void pointer

Author: sahilbansal17

Diff for: Day 16/README.md

@@ -0,0 +1,6 @@
+## Day 16 Programs
+
+1. [Understanding Unions and Enumerations](enum.c)
+2. [Struct, union and enum all at once](fruitOrder.c)
+3. [Void pointer](voidPointers.c)
+4. [Program for generic sum function (to debgug)](genericSum.c)

Diff for: Day 16/enumAndUnion.c

@@ -0,0 +1,33 @@
+/*
+ * Understanding enum and union in C
+ * and also how we can use enums to
+ * know which field of the union has been stored in the memory
+ */
+
+#include <stdio.h>
+
+enum week_day_type {NUMBER, STRING};
+
+typedef union {
+	int week_no;
+	char week_str[10];
+} week_day;
+
+int main () {
+
+	// week_day_type is our custom data type
+	// that can take only the values from the list declared
+
+	enum week_day_type currentDay = STRING;
+	// printf("%d", currentDay);
+
+	week_day tuesday = {.week_str = "TUESDAY"};
+	if (currentDay == STRING) {
+		printf("Current day is: %s\n", tuesday.week_str);
+	}
+	else {
+		printf(" %d\n", tuesday.week_no);
+	}
+
+	return 0;
+}

Diff for: Day 16/fruitOrder.c

@@ -0,0 +1,48 @@
+/*
+ * Program with enum, struct and union
+ */
+
+#include <stdio.h>
+
+typedef enum {
+	COUNT, POUNDS, PINTS
+} unit_of_measure;
+
+typedef union {
+	short count;
+	float weight;
+	float volume;
+} quantity;
+
+typedef struct {
+	const char *name;
+	const char *country;
+	// union type: quantity
+	quantity amount;
+	// enum type: unit_of_measure
+	unit_of_measure units;
+} fruit_order;
+
+void display(fruit_order order) {
+	printf("This order contains ");
+	if (order.units == PINTS) {
+		printf("%2.2f pints of %s\n", order.amount.volume, order.name);
+	} else if (order.units == POUNDS) {
+		printf("%2.2f lbs of %s\n", order.amount.weight, order.name);
+	} else {
+		printf("%i %s\n", order.amount.count, order.name);
+	}
+}
+
+int main() { 
+	fruit_order apples = {"apples", "England", .amount.count = 144, COUNT};
+
+	fruit_order strawberries = {"strawberries", "Spain", .amount.weight = 17.6, POUNDS};
+
+	fruit_order oj = {"orange juice", "U.S.A", .amount.volume = 10.5, PINTS};
+
+	display(apples);
+	display(strawberries);
+	display(oj);
+	return 0;
+}

Diff for: Day 16/genericSum.c

@@ -0,0 +1,44 @@
+/*
+ * Using void pointers to create a generic function
+ */
+
+// TRY TO DEBUG THIS PROGRAM, IT GIVES INCORRECT OUTPUT
+
+#include <stdio.h>
+
+// add function takes in two numbers and prints the result
+// type = 1 => int, type = 2 => float
+void add(void *num1, void *num2, int type) {
+	if (type == 1) {
+		int val1 = *((int *)num1);
+		int val2 = *((int *)num2);
+		printf("The sum is: %d\n", val1 + val2);
+	} else if (type == 2) {
+		float val1 = *((float *)num1);
+		float val2 = *((float *)num2);
+		printf("The sum is: %f\n", val1 + val2);
+	}
+	return ;
+}
+
+int main () {
+	void *a, *b, *c, *d;
+
+	int num1 = 2;
+	a = &num1;
+
+	int num2 = 3;
+	b = &num2;
+
+	float num1f = 2.35;
+	float num2f = 5.1;
+	c = &num1f;
+	d = &num2f;
+
+	// add two integers
+	add(&a, &b, 1);
+	// add two floats
+	add(&c, &d, 2);
+
+	return 0;
+}

Diff for: Day 16/voidPointers.c

@@ -0,0 +1,16 @@
+/*
+ * Program to understand void pointers in C
+ */
+
+#include <stdio.h>
+
+int main () {
+
+	void *ptr;
+	int a = 3;
+	// make the pointer ptr point to an integer
+	ptr = &a;
+	// must type case void pointer to dereference it
+	printf("The value stored in object pointed by ptr is: %d\n",*((int*)ptr));
+	return 0;
+}

Diff for: README.md

@@ -118,4 +118,10 @@ Simple program using if: [if](Day 3/if.c)
 ## Day 15: Structures in C
 1. [Declaring and using structure](Day 15/structFish.c)
 2. [Nested structures](Day 15/nestedStructures.c)
-3. [Updating structure fields](Day 15/turtleBirthday.c)
+3. [Updating structure fields](Day 15/turtleBirthday.c)
+
+## Day 16 Unions, Enum and Void pointers
+1. [Understanding Unions and Enumerations](Day 16/enum.c)
+2. [Struct, union and enum all at once](Day 16/fruitOrder.c)
+3. [Void pointer](Day 16/voidPointers.c)
+4. [Program for generic sum function (to debgug)](Day 16/genericSum.c)