usr/lib/learn/C/L37.1a

#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