乘法变量时的错误答案

Question

I'm trying to multiply two variables. One is an int and the other is inside a char array.

My code is this

int biggestProduct = 1;
int currProduct = 1;
char[] array = num.toCharArray();

for (int x = 0; x < array.length; x++) {
    if (x < 5) {
        System.out.println(currProduct + " * " + array[x] + " = " + currProduct * array[x]);
        currProduct *= array[x];
    }
}

return biggestProduct;

The problem is with the currProduct*= array[x]

This is my output when I print it out:

1 * 7 = 55
55 * 3 = 2805
2805 * 1 = 137445
137445 * 6 = 7422030
7422030 * 7 = 408211650

Why isn't it multiplying correctly?

Answer 1

The problem is that the numeric value of the char 7 is not 7 but 55 .

Because in Java, the char data type is a single 16-bit Unicode character (see encoding table below).

If you take a look at this table, you see that 7 is encoded as 0x0037 = 3*16^1 + 7 = 55 .

If you want to take the real numeric value of your character, you can use Character.getNumericValue(char ch) :

 char ch = '7';
 int number = Character.getNumericValue(ch);
 System.out.print(number); //print 7

So to edit your code, it will looks like :

        String num = "73167";
        int biggestProduct = 1;
        int currProduct = 1;
        char[] array = num.toCharArray();

        for (int x = 0; x < array.length; x++) {
            if (x < 5) {
                System.out.println(currProduct + " * " + array[x] + " = " + currProduct * Character.getNumericValue(array[x]));
                currProduct *= Character.getNumericValue(array[x]);
            }

        }

Output :

1 * 7 = 7
7 * 3 = 21
21 * 1 = 21
21 * 6 = 126
126 * 7 = 882

Verification : 7*3*1*6*7 = 882

Answer 2

Try like this:

currProduct *= (int) array[x];

Check here for what the char values usually represent. You will see that if you want your char to hold the numerical value 2, you have to actually assign 50:

char two = 50;
System.out.println(two); // prints out 2

Answer 3

The value of '7' is 55 because it is just another character like eg 'a', so its numeric value will be its ASCII code. See here: http://www.asciitable.com/
(Note that the used ASCII table can be also implementation dependant.)

Answer 4

The numeric value of '7' isn't 7, it's 55. This is like any character, for example the character 'A' is 65

For example

public class Calendar
{
    public static void main(String[] args){
        char testChar='7';
        int testInt=testChar;

        System.out.println(testInt); //prints 55
    }
}