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week1/task3.c

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+/*
+ * Author: Walter
+ * Student ID: 1930006025
+ * Week_1_Task_3
+ * Read in and compute the greatest common divisor (GCD) of
+ * two natural numbers using recursion
+ */
+
+#include <stdio.h>
+#include <assert.h>
+
+int GCD(int x, int y);
+
+/* the real GCD function */
+int _GCD(int x, int y);
+
+int main() {
+	int x, y;
+	printf("Please input x\n");
+	scanf("%d", &x);
+	printf("Please input y\n");
+	scanf("%d", &y);
+	printf("Result is %d\n", GCD(x, y));
+	return 0;
+}
+
+int GCD(int x, int y) {
+	/* check x y are natural numbers */
+	assert(x >= 0);
+	assert(y >= 0);
+
+	/* make sure x >= y,
+	 * then call the read GCD function */
+	if (x >= y) {
+		return _GCD(x, y);
+	} else {
+		return _GCD(y, x);
+	}
+}
+
+int _GCD(int x, int y) {
+	/* end of recursion */
+	if (y == 0) {
+		return x;
+	}
+
+	return _GCD(y, x % y);
+}