Converting a decimal to a hexadecimal number

Question

Why we use + 55 for converting decimal to hex num . in this code we use +48 to convert integer to character . when temp < 10 . But when temp > =10 we use +55 . what does it mean by +55 ?

#include<stdio.h>
int main(){
    long int decimalNumber,remainder,quotient;
    int i=1,j,temp;
    char hexadecimalNumber[100];

    printf("Enter any decimal number: ");
    scanf("%ld",&decimalNumber);

    quotient = decimalNumber;

    while(quotient!=0){
         temp = quotient % 16;

      //To convert integer into character
      if( temp < 10)
           temp =temp + 48;
      else
         temp = temp + 55;

      hexadecimalNumber[i++]= temp;
      quotient = quotient / 16;
  }

    printf("Equivalent hexadecimal value of decimal number %d: ",decimalNumber);
    for(j = i -1 ;j> 0;j--)
      printf("%c",hexadecimalNumber[j]);

    return 0;
}

Answer 1

In an ASCII environment, 55 is equal to 'A' - 10. This means that adding 55 is the same as subtracting 10 and adding 'A'.

In ASCII, the values of 'A' through 'Z' are adjacent and sequential, so this will map 10 to 'A', 11 to 'B' and so on.

Answer 2

For values of temp less than 10, the appropriate ASCII code is 48 + temp:

0 => 48 + 0 => '0'
1 => 48 + 1 => '1'
2 => 48 + 2 => '2'
3 => 48 + 3 => '3'
4 => 48 + 4 => '4'
5 => 48 + 5 => '5'
6 => 48 + 6 => '6'
7 => 48 + 7 => '7'
8 => 48 + 8 => '8'
9 => 48 + 9 => '9'

For values 10 or greater, the appropriate letter is 55 + temp:

10 => 55 + 10 => 'A'
11 => 55 + 11 => 'B'
12 => 55 + 12 => 'C'
13 => 55 + 13 => 'D'
14 => 55 + 14 => 'E'
15 => 55 + 15 => 'F'

Answer 3

Because of the ASCII encoding of characters in C. When the remainder (temp) is less than ten, the digit in the hexadecimal is also in the range of 0 to 9. The characters '0' to '9' are on the ASCII range of 48 to 57.

When the remainder is more than 10 (and always less than 15, due to the remainder operation %) the hexadecimal digit is in the range A to F, which in ASCII is in the range of 65 to 70. So temp + 55 is a number from 65 to 70 and thus gives a character in the range of 'A' to 'F'.

It is more common to use a string char[] digits = "0123456789ABCDEF"; and use the remainder as an index in this string. The method in your question (probably) works as well though.

Answer 4

Hexadecimal number is a number represented using 16 symbols which are 0 -9 numbers and A – F alphabets. Procedure to write a c program to convert decimal number to hexadecimal is: Divide the decimal number with 16 at each step and take remainders

Here for remainders 0 – 9 numbers are used and then to represent 10 to 15 numbers we use alphabets A, B, C, D, E, F . Now combine all remainders serially from down to up i.e A This is hexadecimal number of 10 (decimal )

eg To convert decimal number 10 to hexadecimal

16 | 10 | 0 – A

Now combine all remainders serially from down to up i.e A . This is hexadecimal number of 10 (decimal )

Program Logic: Enter decimal number n, divide n by 16 ( since hexadecimal ) and save remainder in array and quotient in n repeat until n is greater than zero

view program at: http://www.programmingsimplysolved.com/c-programs/c-program-to-convert-decimal-number-to-hexadecimal-using-functions/

contributed by: www.programmingsimplysolved.com