How does one convert ASCII to binary?

I have the following string:

char * strIn = "f2";

When I look at strIn[0] I would like to get 1111 instead of 'f'.

How do i do it?

开发者_StackOverflow中文版Thanks

---

You mean a hex string to binary conversion?

strtol with a base of 16 should do the trick

---

...Someone said earlier

and f in binary would be 11001100

All I can say is wow... no, F in binary equals 1111 (15 decimal)

If I understood your question correctly, you want to get the binary value for any ascii character... ie.

When I look at strIn[0] I would like to get 1111 instead of 'f'.

So... here is a little function that will do that...

int ConvertHexAsciiValue(char c)
{
    if(isalpha(c))
    {
        char r = tolower(c);
        if(r > 'f')
        {
            // - Handle error here - character is not base 16
            return 0;
        }

        int nIndex = (int)('a' - r);
        nIndex = -nIndex;
        nIndex += 10;
        return nIndex;
    }
    else if(isdigit(c))
    {
        int nIndex = c - '0';
        return nIndex;
    }

    // Handle error here - character is not A-F or 0-9
    return 0;
}

If I didn't understand you correctly, you should know that you cannot read a string "1111" for a character strIn[0]. You can however, get a binary value for each character (interpreted as a hexidecimal value) using the function I provided...

 for(int x = 0; x < strlen(strIn); x++)
 {
     int val = ConvertHexAsciiValue(strIn[x]);
     printf("Value %d: %d\n", x, val); 
 }

If strIn were set to "f2", this code would produce the following output on the console

Value 0: 15
Value 1: 2

---

To get the binary code one must take the decimal number in question, take it and divide it by two repeatedly, save the remainder (which will become the binary number), save the whole number, divide by two, and repeat the whole process until 0 is reached.

Heres a small application I had in my collection that converts a string into binary.

/********************************************************/
/*                    Binary converter                  */
/*                     By Matt Fowler                   */
/*                philosopher150@yahoo.com              */
/*  converts text into binary using the division method */
/*                   through ASCII code                 */
/*compiled with the Dev-C++ compiler (www.bloodshed.net)*/
/********************************************************/

#include <iostream>
using namespace std;
#include <cstring>
#include <cstdlib>

char *entry, letter, choice[2];
int ascii, len, binary[8], total;
void prog();

int main()
{
      prog();     
      return 0;
}        

void prog()
{
   entry = new char[501];

   /* entry should be dynamic, otherwise a new string entry of 501 chars would be created each time function is called! Talk about memory hog! */

   cout<<"Enter string to convert (up to 500 chars): ";

   cin.getline(entry, 500);
   len = strlen(entry);  /* get the number of characters in entry. */

   /* this loop is executed for each letter in the string. */
   for(int i = 0; i<len; i++)
   {
      total = 0;
      letter = entry[i]; /* store the first letter */
      ascii = letter;    /* put that letter into an int, so we can                                 see its ASCII number */

      while(ascii>0) /* This while loop converts the ASCII # into binary,                             stores it backwards into the binary array. */
      {
      /* To get the binary code one must take the decimal number in
        question, take it and divide it by two repeatedly, save
        the remainder (which will become the binary number), save
        the whole number, divide by two, and repeat the whole
        process until 0 is reached.  This if-else statement serves
        this functionality, by getting the remainder of the ascii
        code, storing it in the array and then dividing the int
        ascii by two */

         if((ascii%2)==0)
         {
            binary[total] = 0;
            ascii = ascii/2;
            total++; /* increasing by one each time will yeild the
                        number of numbers in the array. */
         }
         else
         {
            binary[total] = 1;
            ascii = ascii/2;
            total++;
         }
      }
      total--; /* due to data type factors, the program will actually
                  add a 0 at the end of the array that is not supposed
                  to be there, decrementing total will solve this
                  problem, as that 0 will not be displayed. */
      /* this while loop displays the binary code for that letter. */
      while(total>=0)
      {
         cout<<binary[total];
         total--;
      }
   }
   delete[] entry; /* free up the memory used by entry */
   cout<<endl<<"Do again(1 = yes, 2= no)?: ";
   cin.getline(choice,3);
   if(choice[0] == '1')
      prog(); /* program is recursive, it calls itself.  It's kinda
                 like a function loop of sorts. */
   else
      exit(0); /* quits the program */  
}