shell_sort.c: Add Shell sort algorithm in C

This implementation uses half of the array's size as the gap.
Then it keeps dividing it by 2.

Closes #135

README.md

@@ -20,7 +20,7 @@ This repository contains examples of various algorithms written on different pro
 | [Radix Sort](https://en.wikipedia.org/wiki/Radix_sort)                                          |                                       |                                       |                                       | [:octocat:](radix_sort/Python)        |
 | [Binary Search](https://en.wikipedia.org/wiki/Binary_search_algorithm)                          |                                       | [:octocat:](binary_search/Cpp)        |                                       | [:octocat:](binary_search/Python)     |
 | [Bubble Sort](https://en.wikipedia.org/wiki/Bubble_sort)                                        | [:octocat:](bubble_sort/C)            | [:octocat:](bubble_sort/Cpp)          |                                       |                                       |
-| [Shell Sort](https://en.wikipedia.org/wiki/Shellsort)                                           |                                       |                                       |                                       | [:octocat:](shell_sort/Python)        |
+| [Shell Sort](https://en.wikipedia.org/wiki/Shellsort)                                           | [:octocat:](shell_sort/C)             |                                       |                                       | [:octocat:](shell_sort/Python)        |
 | [Heap Sort](https://en.wikipedia.org/wiki/Heapsort)                                             |                                       |                                       |                                       | [:octocat:](heap_sort/python)        |
 
 

shell_sort/C/shell_sort.c

@@ -0,0 +1,30 @@
+#include <stdio.h>
+
+void shellsort(int size, int *arr) {
+	// start with a big gap and reduce it
+	for (int gap = size/2; gap > 0; gap = gap/2) {
+		for (int i = gap; i < size; i = i+1) {
+			int temp = arr[i];
+
+			int j;
+			// shifting elements until the location for arr[i] is found
+			for (j = i; j >= gap && arr[j-gap] > temp; j = j-gap) {
+				arr[j] = arr[j-gap];
+			}
+			arr[j] = temp;
+		}
+	}
+}
+
+int main() {
+	int arr_size = 6;
+	int arr[6] = {10, 9, 8, 7, 6, 5 };
+	shellsort(arr_size, arr);
+
+	for (int i = 0; i < arr_size; i++) {
+		printf("%d ", arr[i]);
+	}
+	printf("\n");
+
+	return 0;
+}