Convert char to int

ianni · 11-12-2014, 11:32 PM

Hello everybody,i have a question,i want to conver character to integer in Java,i find this and it s working but i cant understand why

I want to take the number 3 and not the ASCII value

char ch = '3';

int num = (ch-48);

why number 48?

Teufel · 11-13-2014, 12:47 AM

Why 48?
48 is the ascii code of '0' symbol.
If you want to replace text representation of digit (human readable) with its integer value (machine readable), you have to subtract the 'base' - ascii code of '0' char, since chars '0' - '9' follows each other
The following explains it:

Code:

 Code    Char
  ..      ..
  ..      ..
  48      '0'
  49      '1'
  50      '2'
  51      '3'
  ..      ..

Here the ascii table:
http://www.cpptutor.com/ascii.htm

a4z · 11-13-2014, 01:21 AM

a short google what atoi in java is brought

Integer.parseInt(String str) and Integer.toString(int integer);

don't use things like int num = (ch-48) in any language, this was the way to do more than 30 years ago, but meanwhile there are library functions for each language to do this

Teufel · 11-13-2014, 03:31 AM

Use ch-48.
It's much less code.
it's much more faster.
It's much more clear.
It gives you an idea of how things work.

NevemTeve · 11-13-2014, 03:34 AM

Actually, it is

Code:

num= ch-'0';

(I, for one, did work in EBCDIC)

ianni · 11-13-2014, 03:47 AM

Quote:

48 is the ascii code of '0' symbol.
If you want to replace text representation of digit (human readable) with its integer value (machine readable), you have to subtract the 'base' - ascii code of '0' char, since chars '0' - '9' follows each other
The following explains it:

Thank you very much my friend,you realy help me

Quote:

a short google what atoi in java is brought

Integer.parseInt(String str) and Integer.toString(int integer);

don't use things like int num = (ch-48) in any language, this was the way to do more than 30 years ago, but meanwhile there are library functions for each language to do this

Thank you to my friend for the answer.I m new in Java and i dont know strings and any other library functions yet.I want to make a simple java calculator but i HAVE to use System.in.read,that s why i need to convert char to int,by the way i made it but the only problem is that i cant give characters more then 9(1-9) with system read.Any ideas?
Here it s my code

Code:

      public static void main(String[] args)throws IOException
      {
              char ch = 0;
              float num1 = 0;
              float num2 = 0;
              float A[] = new float[3];
              
              for(int i=0; i<3; i++)
              {
                  A[i] = System.in.read();
              }
              
              
              for(int i=0; i<3; i++)
              {
                  if(A[i] >= 48 && A[i] <= 57)  
                  {
                      A[i] = A[i] - 48;
                      num1 = A[0];
                      ch = (char)A[1];
                      num2 = A[2];
                  } 
              }   
                      switch(ch)
                      {
                          case '+':
                              System.out.println(num1+num2);
                          break;  
                              
                          case '-':
                              System.out.println(num1-num2);
                          break;
                              
                          case '*':
                              System.out.println(num1*num2);
                          break;  
                               
                          case '/':
                              if(num2 == 0)
                              {
                                  System.out.println("cant divide with 0");
                              }
                              
                              else
                              {
                                  System.out.println(num1/num2);
                              }
                              
                          break;
                              
                          default:
                              System.out.println("bye bye");
                          break;  
                      }
                  }
              }

rtmistler · 11-13-2014, 12:56 PM

Quote:

Originally Posted by ianni

the only problem is that i cant give characters more then 9(1-9) with system read.Any ideas?

Not sure if the problem is that you can't "enter" things like A, B, C, D, E, and F to make hex numbers; or if you have problems with converting those numbers. On the conversion part, you can subtract '0', or in my viewpoint 0x30 and if the number is larger than 9, subtract 7.

ASCI A is 0x41
Subtract 0x30 gives you 0x11
0x11 is Decimal 17.
Subtracting 7 gives you 10, decimal. Which is what 0xA represents

The same works for A-F HEX digits.

Here's a very good ASCII table which I think has been online for like 10 or more years, I've used it for a very long period of time: http://web.cs.mun.ca/~michael/c/ascii-table.html

smeezekitty · 11-13-2014, 01:03 PM

Quote:

Originally Posted by NevemTeve

Actually, it is

Code:

num= ch-'0';

(I, for one, did work in EBCDIC)

That would be a little safer. still subtracting a fixed number to convert between "text" representation and numeric representation might not
be the most reliable. It is easy though. I am not sure if it will work with wide chars. Also, you need to make sure it is in range (i.e. '0'-'9') or you will get weird results.

NevemTeve · 11-13-2014, 01:22 PM

Well, perhaps it is strtol (or a cousin of that) the OP is looking for. (Edit: if it were C-language, that is.)

smeezekitty · 11-13-2014, 01:46 PM

Hmmm. It says "in Java"

Maybe Integer.valueOf is what you are looking for?
I don't know much about Java but being a very HLL I am sure there is a better way to do this.