1 files changed, 105 insertions, 0 deletions
diff --git a/numbers-thing/numbers-thing.c b/numbers-thing/numbers-thing.c
new file mode 100644
index 0000000..e523828
--- /dev/null
+++ b/numbers-thing/numbers-thing.c
@@ -0,0 +1,105 @@
+#include <stdio.h>
+
+enum operator {
+	OP_MULTIPLY,
+	OP_DIVIDE,
+	OP_ADD,
+	OP_SUBTRACT,
+	OP_IDENTITY /* marks leaves */
+};
+
+struct bnode {
+	int value;
+	enum operator operator;
+	struct bnode *left;
+	struct bnode *right;
+};
+
+char
+op_lookup(enum operator op) {
+	switch (op) {
+		case OP_MULTIPLY: return '*';
+		case OP_DIVIDE:   return '/';
+		case OP_ADD:      return '+';
+		case OP_SUBTRACT: return '-';
+		default:
+			/* FIXME return this, error out somehow else? */
+			return '?';
+	}
+}
+
+double
+evaluate_op(double left, enum operator op, double right) {
+	switch(op) {
+		case OP_MULTIPLY: return left * right;
+		case OP_DIVIDE:   return (double)left / right;
+		case OP_ADD:      return left + right;
+		case OP_SUBTRACT: return left - right;
+		default:
+			/* FIXME return nan */
+			return -100000;
+	}
+}
+
+double
+evaluate(struct bnode* node) {
+	if (node->operator == OP_IDENTITY)
+		return node->value;
+
+	/* FIXME could/should NULL-check children
+	 * Non-identity node should have two childre, but I might manage to
+	 * screw it up somehow eh */
+	return evaluate_op(
+		evaluate(node->left),
+		node->operator,
+		evaluate(node->right));
+}
+
+void
+dump_tree(struct bnode *node) {
+	if (node->operator == OP_IDENTITY) {
+		printf("%d", node->value);
+		return;
+	}
+
+	printf("(");
+	if (node->left != NULL)
+		dump_tree(node->left);
+
+	printf(" %c ", op_lookup(node->operator));
+
+	if (node->right != NULL)
+		dump_tree(node->right);
+	printf(")");
+}
+
+int
+main(int argc, char **argv) {
+	struct bnode a,b,c,d,e, o1,o2,o3,o4;
+
+/*	((1+2)/(3*(4-5))) */
+	a.value = 1; a.operator = OP_IDENTITY; a.left = a.right = NULL;
+	b.value = 2; b.operator = OP_IDENTITY; b.left = b.right = NULL;
+	c.value = 3; c.operator = OP_IDENTITY; c.left = c.right = NULL;
+	d.value = 4; d.operator = OP_IDENTITY; d.left = d.right = NULL;
+	e.value = 5; e.operator = OP_IDENTITY; e.left = e.right = NULL;
+
+	o1.left  = &a;
+	o1.right = &b;
+	o1.operator = OP_ADD;
+
+	o2.left = &d;
+	o2.right = &e;
+	o2.operator = OP_SUBTRACT;
+
+	o3.left = &c;
+	o3.right = &o2;
+	o3.operator = OP_MULTIPLY;
+
+	o4.left = &o1;
+	o4.right = &o3;
+	o4.operator = OP_DIVIDE;
+
+	dump_tree(&o4);
+	printf("\n = %f\n", evaluate(&o4));
+}