C

DeitelC/Chapter5/exercise5-43.c

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+#include <stdio.h>
+int mystery(int a, int b); // function prototype
+
+int main(void) {
+	printf("%s", "Enter two positive integers: ");
+	int x = 0; // first integer
+	int y = 0; // second integer
+	scanf("%d%d", &x, &y);
+	printf("The result is %d\n", mystery(x, y));
+}
+
+// Parameter b must be a positive integer
+// to prevent infinite recursion
+int mystery(int a, int b) {
+// base case
+	if (1 == b) {
+		return a;
+	} else if (b > 1) { // recursive step
+		return a + mystery(a, b - 1);
+	} else {
+		return -a + mystery(a, b + 1);
+	}
+}