我的方法有什么问题？

Question

I just wanted to create a method which can convert a number from binary system(base2) to decimal system(base10). But I come up with some problems. I don't know how to correct it. Here is my method

public static int toDecimal (String base2) 
   {
     int sum=0;

     for ( int k=base2.length(); int i=0; k>0, i<=base2.length()-1; k--, i++)
     {
       char symbol = base2.charAt(k);
       sum= sum+ symbol*i;
     }
     return sum;
   }

PS: I could not be able to convert a character to integer type (sum+ symbol*i;) . If possible, could you also give some advice about it.

Answer 1

Actually your code is not working because of incorrect for loop syntax - you can use ; symbol only two times inside the parentheses. Also sum = sum + symbol * i; is not right coversion formula.

It seems that this code resolves your problem

public static int toDecimal(String base2) {
    int sum=0;
    int i = 0;
    for (int k = base2.length() - 1; k >= 0; k--) {
        sum += Integer.parseInt(String.valueOf(base2.charAt(k))) << i;
        i++;
    }
    return sum;
}

I hope that this helps you!

Answer 2

just some minor changes to your for loop will get the code working

public static int toDecimal(String base2) {
    int sum = 0;    
    for (int k = base2.length() - 1, i = 0; k>=0; k--, i++) {
        int symbol = (int)base2.charAt(k)-48;//0 is 48; 1 is 49 in ASCII
        sum = (int) (sum + (int) symbol * Math.pow(2, i));
    }
    return sum;
}

here you go

Answer 3

In you for loop you initialize 2 variables. Between them you have a ; (semicolon) but there should be a , (comma).

Answer 4

To eliminate the need for the parseInt call, and to start from the beginning of the string, you can use

   public static int toDecimal( String str) {
      int val = 0;
      for (int i = 0; i < str.length(); i++) {
         val = (val<<1) + ((str.charAt( i ) == '0') ? 0 : 1);
      }
      return val;
   }