Add c/difference-of-squares

Work-in-progress.

c/difference-of-squares/src/difference_of_squares.c

@@ -0,0 +1,17 @@
+#include <stdio.h>
+#include <math.h>
+
+int square_of_sum(int n) {
+	int sum = (int) (n * ((n * 0.5) + 0.5));
+	return pow(sum, 2);
+}
+
+int sum_of_squares(int n) {
+	printf("%d\n", n);
+	return n;
+}
+
+int difference_of_squares(int n) {
+	printf("%d\n", n);
+	return square_of_sum(n) - sum_of_squares(n);
+}

c/difference-of-squares/src/difference_of_squares.h

@@ -0,0 +1,5 @@
+int square_of_sum(int n);
+
+int sum_of_squares(int n);
+
+int difference_of_squares(int n);