import BTL learn(1) lessons/C

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+#print
+Let's try a recursive function.  Write a subroutine
+    power(x,n)
+which computes x to the power n by the following
+algorithm:
+ 1. if n is zero return 1.
+ 2. if n is odd return x*power(x,n-1).
+ 3. if n is even return the square of
+    power(x,n/2).
+You may assume than x and n are integers, n>=0.
+If n is negative return 0 for an answer.
+Put your routine on a file "power.c".  Compile
+it and test it; then type "ready".
+#once #create tzaqc.c
+main()
+{
+if (power(-1,-1) != 0) 
+		return(1);
+	if (power(-3,2) != 9) 
+		return(1);
+	if (power(2,12) != 4096) 
+		return(1);
+	if (power(3,5) !=  243) 
+		return(1);
+	if (power(-5, 5) != -3125) 
+		return(1);
+	if (power(7,3) != 343) 
+		return(1);
+	if (power(7,4) != 2401) 
+		return(1);
+	if (power(3,7) != 2187) 
+		return(1);
+	if (power(2,10) != 1024) 
+		return(1);
+	return(0);
+}
+#user
+cc tzaqc.c power.o
+a.out
+#succeed
+/*  a possible solution */
+power(x, n)
+{
+	int k;
+
+	if (n < 0)
+		return(0);
+	if (n == 0)
+		return(1);
+	if (n%2 == 1)
+		return(x * power(x, n-1));
+	k = power(x, n/2);
+	return(k*k);
+}
+#log
+#next
+40.1a 10