Weird thing convert float to binary

Hi,
Could someone please take a look at this function I don't know why it is not working. The compiler just hangs.

Code:

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void dectohex (float num);
int main(int argc, char** argv)
{
  float num2;
    if (argc >= 2)
      num2 = atof(argv[1]);
    else
      scanf("%2.1f", &num2);


dectohex(num2);

}

void dectohex (float num)
{
  float num1;
  int int_part;
  unsigned int i, pos = sizeof(int)*8 - 1;
  const unsigned int int_msb = 1 << (sizeof(int)*8 - 1);
  int_part = num1;
  num1 -= int_part;
 
if (int_part < 0) {
    putc('-', stdout);
    int_part = -int_part;
    num1 = -num1;
}


for (i = 0; pos; i ++, pos --) {
    if (int_part & (int_msb >> i))
    break;
}
for (; pos; pos --) {
    putc(((int_part & (1 << pos)) >> pos) + '0', stdout);
                        }
putc((int_part & 1)+ '0', stdout);

if (num1)
  putc('.', stdout);
  while (num1) {
  num *= 2;
  putc(((int) num1 & 1), stdout);
  num1 -= (int) num1;
  }
}

---

If your compiler hangs when trying to compile a program, I suggest you start using a new compiler.

It compiles fine for me except #include <stdio.h> needs to be added.

There are also a few wrong things, such as %2.1f not making sense for a format specifier in your scanf.

Also, you can indent code how you like, but when you post code expecting people to look at it, I would suggest you indent it in a reasonable manner.

I am using Cygwin. Are you getting the correct output.thanks for the suggestion I indented the code.

Quote:

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Originally Posted by sara.stanley

Are you getting the correct output.

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Nope.

do you know what the problem is.

1. Enable all the warnings, eg.

Code:

---

$ gcc bar.c
$ gcc -W -Wall -ansi -pedantic -O2 bar.c
bar.c: In function `main':
bar.c:9: warning: implicit declaration of function `atof'
bar.c:11: warning: unknown conversion type character `.' in format
bar.c:11: warning: too many arguments for format
bar.c: In function `dectohex':
bar.c:17: warning: 'num1' might be used uninitialized in this function
bar.c: In function `main':
bar.c:13: warning: control reaches end of non-void function

---

2. Lack of indentation, and omitting braces where you think they are optional (when in fact they are not) will kill you every time.

Code:

---

#include <stdio.h>

void dectohex(float num);

int main(int argc, char **argv)
{
    float num2;
    if (argc >= 2)
        num2 = atof(argv[1]);
    else
        scanf("%2.1f", &num2);
    dectohex(num2);
}

void dectohex(float num)
{
    float num1;
    int int_part;
    unsigned int i, pos = sizeof(int) * 8 - 1;
    const unsigned int int_msb = 1 << (sizeof(int) * 8 - 1);
    int_part = num1;
    num1 -= int_part;

    if (int_part < 0) {
        putc('-', stdout);
        int_part = -int_part;
        num1 = -num1;
    }


    for (i = 0; pos; i++, pos--) {
        if (int_part & (int_msb >> i))
            break;
    }

    for (; pos; pos--) {
        putc(((int_part & (1 << pos)) >> pos) + '0', stdout);
    }
    putc((int_part & 1) + '0', stdout);

    if (num1)
        putc('.', stdout);

    while (num1) {
        num *= 2;
        putc(((int) num1 & 1), stdout);
        num1 -= (int) num1;
    }
}

---

Can you now spot the infinite loop?

thanks, the programs ends but I still don't get the correct result.

just compare my code with yours to see what you've done wrong.

i like how you intend to find the binary code after the decimal.

i suggest you put comments in your program. since there wasn't any i relied of the names (int_part was particularly helpful), i had to guess what num1 was, lucky i guessed right.

Code:

---

#include <stdio.h>
#include <ctype.h>

void dectohex (float num);

int main(int argc, char* argv) { // yours was int main(int argc, char** argv) {
    float num2;
    if (argc >= 2) num2 = atof(argv[1]);
    else scanf("%f", &num2); /* you had else scanf("%2.1f", &num2); the number
                            between the % and f must be an integer and suggests
                            maximum number of digits + '.' to be read */
   
    dectohex(num2);
   
    system("PAUSE");
    return 0;
}

void dectohex (float num)
{
    float num1;
    int int_part;
    unsigned int i, pos = sizeof(int)*8 - 1;
    const unsigned int int_msb = 1 << (sizeof(int)*8 - 1);
   
    /* you had int_part = num1; num1 -= int_part;
    which you can't do because you haven't declared a value for num1 */
    int_part = (int)num;
    num1 = num;
    num1 -= int_part;
 
    if (int_part < 0) {
        putc('-', stdout);
        int_part = -int_part;
        num1 = -num1;
    }

    // finds first set bit in int_part
    for (i = 0; pos; i ++, pos --) if (int_part & (int_msb >> i)) break;
   
    // display binary code for int_part
    for (; pos; pos --) putc(((int_part & (1 << pos)) >> pos) + '0', stdout);
    putc((int_part & 1)+ '0', stdout);
 
    // displays decimal point
    if (num1) putc('.', stdout);
   
    /* displays binary code after decimal place,
      might want to put a restriction on this because of float's
      precision which will lead to incorrect binary code
      or change to a double. maybe even an infinite loop*/
    while (num1) {
        num1 *= 2;                              // you had num *= 2;
        putc(((int)num1 & 1)+'0', stdout);      // you forgot + '0'
        num1 -= (int)num1;
    }
}

---

When you convert the program to a seperate function you wouldn't need to declare any float for the new function as the float value is being declared as a formal parameter so the num1 is unnecessary.

[edit] Here's some explanation of the variables meaning and some comments in the code.
num = The number.
int_part = The integer part of num
i = Index, used for incrementation of loops
pos = The current bit position when processing the integer part
int_msb = Most Significant Bit for the integer type, i.e the highest bit will be set to 1 and the rest 0 so when int is 32-bit it will look like 10000000 00000000 00000000 00000000

Code:

---

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

void dectobin (float num);

int main (int argc, char** argv)
{
        float num;

        if (argc >= 2)
                num = atof(argv[1]);
        else
                scanf("%f", &num);       
        dectobin(num);

        return 0;
}

void dectobin (float num)
{
                      int int_part;
              unsigned int i, pos = sizeof(int)*8 - 1;
        const unsigned int int_msb = 1 << (sizeof(int)*8 - 1);

        /* Splits the number into an integer part and decimal part, this is
        * done because we need to know where to put the '.'
        */
        int_part = num;
        num -= int_part;

        //If the number is negative, change it to positive and write '-' character.
        if (int_part < 0) {
                putc('-', stdout);
                int_part = -int_part;
                num = -num;
        }

        /* Find out where to start, i.e. where the first '1' bit is
        * Otherwise we'd probably get a long zerofill.
        */
        for (i = 0; pos; i++, pos--) {
                if (int_part & (int_msb >> i))
                        break;
        }

        //Traverses the integer part and writes it's binary.
        for (; pos; pos--) {
                putc(((int_part & (1 << pos)) >> pos) + '0', stdout);
        }

        /* pos needs to be 0 for the least significant bit, but that ends the loop.
        * Also, this will ensure a 0 in front of a possible '.' so that
        * 0.625 becomes "0.101" and not ".101"
        */
        putc((int_part & 1) + '0', stdout);

        //Don't make me explain this.
        if (num)
                putc('.', stdout);

        //Finally prints out the decimal part.
        while (num) {
                num *= 2;
                putc(((int) num & 1) + '0', stdout);
                num -= (int) num;
        }
}

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Thanks a lot for all your help.