Simple Java power recursion

Question

So the recursive function I'm making takes 2 variables (x and y) and calculates x to the power of y. Just like the Math.pow function. y is positive, so I don't need to worry about negative exponents. This is my code:

public static int power(int x, int y) {     
    if (y == 0)         
        return 1;           
    else        
        return x * power(x, y-1);
}

At first it seemed like it worked fine, but then I tried to enter power(50,6). I got -1554869184. Obviously this is wrong because the correct answer can't be negative.

What is the largest possible integer value? What is the value of 50^6? en.wikipedia.org/wiki/Integer_overflow — JB Nizet
– JB Nizet, Commented Sep 14, 2014 at 16:47
Use Long instead of int. int can't store such large reuslt stackoverflow.com/questions/15004944/max-value-of-integer — anjibcs
– anjibcs, Commented Sep 14, 2014 at 16:50
Thanks I understand it now. I'm sorry I'm new to all of this. I feel so dumb now :) — niana
– niana, Commented Sep 14, 2014 at 16:52

ROMANIA_engineer · Accepted Answer · 2014-11-02 11:12:18Z

2

Your method is good, but it doesn't work for numbers that are too long.

int has 4-bytes (32 bits) => the maximum value is 2147483647 ( 2^31-1 ), total: 2^32 values (there are also some negative numbers)

long has 8-bytes (64 bits) => the maximum value is 9223372036854775807 ( 2^63-1 ), total: 2^64 values

Those values can be found in Java using:

Integer.MAX_VALUE     // Integer and int have the same range
Long.MAX_VALUE        // Long and long have also the same range

For your case: 50^6 = 15625000000 is a valid long number, but not a valid int (it's bigger than 2^32-1 )

Be careful:

If you try to use numbers that are longer you can have problems with long, too. E.g.:

power(10,18);  // OK
power(10,19);  // not OK: negative number
power(10,20);  // not OK: even if the number is positive
               //         the answer is not good - it has only 18 digits!

edited Nov 2, 2014 at 11:12

answered Sep 14, 2014 at 16:54

ROMANIA_engineer

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