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Annotation of 42BSD/usr.lib/learn/C/L37.1a, revision 1.1.1.1

1.1       root        1: #print
                      2: Let's try a recursive function.  Write a subroutine
                      3:     power(x,n)
                      4: which computes x to the power n by the following
                      5: algorithm:
                      6:  1. if n is zero return 1.
                      7:  2. if n is odd return x*power(x,n-1).
                      8:  3. if n is even return the square of
                      9:     power(x,n/2).
                     10: You may assume than x and n are integers, n>=0.
                     11: If n is negative return 0 for an answer.
                     12: Put your routine on a file "power.c".  Compile
                     13: it and test it; then type "ready".
                     14: #once #create tzaqc.c
                     15: main()
                     16: {
                     17: if (power(-1,-1) != 0) 
                     18:                return(1);
                     19:        if (power(-3,2) != 9) 
                     20:                return(1);
                     21:        if (power(2,12) != 4096) 
                     22:                return(1);
                     23:        if (power(3,5) !=  243) 
                     24:                return(1);
                     25:        if (power(-5, 5) != -3125) 
                     26:                return(1);
                     27:        if (power(7,3) != 343) 
                     28:                return(1);
                     29:        if (power(7,4) != 2401) 
                     30:                return(1);
                     31:        if (power(3,7) != 2187) 
                     32:                return(1);
                     33:        if (power(2,10) != 1024) 
                     34:                return(1);
                     35:        return(0);
                     36: }
                     37: #user
                     38: cc tzaqc.c power.o
                     39: a.out
                     40: #succeed
                     41: /*  a possible solution */
                     42: power(x, n)
                     43: {
                     44:        int k;
                     45: 
                     46:        if (n < 0)
                     47:                return(0);
                     48:        if (n == 0)
                     49:                return(1);
                     50:        if (n%2 == 1)
                     51:                return(x * power(x, n-1));
                     52:        k = power(x, n/2);
                     53:        return(k*k);
                     54: }
                     55: #log
                     56: #next
                     57: 40.1a 10

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