Have problem converting a decimal number to octal

Linh · 05-20-2004, 02:36 PM

Have problem converting a decimal number to octal
the decimal number is 408.
When converting from 408(decimal) to octal, the value should be 630 (octal)
but instead it gives a value of 40 or 32.

====================================
root:/home# ./convert_a_decimal_to_octal

decimal_char = 408
decimal_number = 408
octal_number = 40
octal_number = 32

====================================

Code:

#include <stdio.h>         
#include <stdlib.h>        
#include <string.h>

/********************************************/

start_processes()
 {
    char decimal_char[4] = "408";
    int decimal_number = 0;
    int octal_number = 0;


    printf ("decimal_char = %s\n", decimal_char);

    /* convert a numeric character to decimal */
    sscanf(decimal_char, "%d", &decimal_number);
    printf ("decimal_number = %d\n", decimal_number);

    /* convert a decimal number to octal    */
     sscanf(decimal_char, "%o", &octal_number);
     printf ("octal_number = %o\n", octal_number);
     printf ("octal_number = %d\n", octal_number);
  }

/********************************************/

main()
  {
    start_processes();
  }

Hko · 05-20-2004, 03:09 PM

"408" is not a valid octal string, because octal uses only 8 digits: '0' to '7'.
So the digit '8' in "408" is not valid for octal conversion so sscanf() stop the conversion after reading "40".

Also you have some other mistakes in the code, though it would work probably.
To see warnings in addition to erros, compile with

Code:

gcc -Wall -pedanic -o convert_a_decimal_to_octal convert_a_decimal_to_octal.c

Fixed code below, changes are in red.

Code:

#include <stdio.h>
#include <stdlib.h>        
#include <string.h>

/********************************************/

void start_processes(void)
{
	 char decimal_char[4] = "407";
	 int decimal_number = 0;
	 unsigned int octal_number = 0;

	 printf ("decimal_char = %s\n", decimal_char);

	 /* convert a numeric character to decimal */
	 sscanf(decimal_char, "%d", &decimal_number);
	 printf ("decimal_number = %d\n", decimal_number);

	 /* convert a decimal number to octal    */
	 sscanf(decimal_char, "%o", &octal_number);
	 printf ("octal_number = %o\n", octal_number);
	 printf ("octal_number = %d\n", octal_number);
}

/********************************************/

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

Mara · 05-20-2004, 03:10 PM

Decimal or octal number, it's kept the sam way. That's displaying that makes the difference...
When you do the sscanf, '408' is taken as an octal number, but it's incorrect (it has '8'), so only two first digits are taken into account.
You get '32' as one of the results, because '32' (decimal) or '40' octal is in octal_number.

You can use

Code:

printf("octal number = %o\n", decimal_number);

without problems.

Mara · 05-20-2004, 03:14 PM

Hko, the orginal author wants decimal->octal, not octal->decimal conversion

Hko · 05-20-2004, 03:21 PM

Oh. That wasn't clear to me then. Maybe Linh should read the other thread again at:
http://www.linuxquestions.org/questi...hreadid=183725