Question

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

int myatoi(const char* string) {
  int i = 0;
  while (*string) {
    i = (i << 3) + (i<<1) + (*string -'0');
    string++;
  }
  return i;
}

void decimal2binary(char *decimal, int *binary) {
  decimal = malloc(sizeof(char) * 32);
  long int dec = myatoi(decimal);
  long int fraction;
  long int remainder;
  long int factor = 1;
  long int fractionfactor = .1;
  long int wholenum;
  long int bin;
  long int onechecker;
  wholenum = (int) dec;
  fraction = dec - wholenum;

  while (wholenum != 0 ) {
    remainder = wholenum % 2;  // get remainder
    bin = bin + remainder * factor;  // store the binary as you get remainder
    wholenum /= 2;  // divide by 2
    factor *= 10;  // times by 10 so it goes to the next digit
  }
  long int binaryfrac = 0;
  int i;
  for (i = 0; i < 10; i++) {
    fraction *= 2;  // times by two first
    onechecker = fraction;  // onechecker is for checking if greater than one
    binaryfrac += fractionfactor * onechecker;  // store into binary as you go
    if (onechecker == 1) {
      fraction -= onechecker;  // if greater than 1 subtract the 1
    }   
    fractionfactor /= 10;
  }

  bin += binaryfrac;
  *binary = bin;
  free(decimal);
}

int main(int argc, char **argv) {   
  char *data;
  data = malloc(sizeof(char) * 32);
  int datai = 1;
  if (argc != 4) {
    printf("invalid number of arguments\n");
    return 1;
  }
  if (strcmp(argv[1], "-d")) {  
    if (strcmp(argv[3], "-b")) {
      decimal2binary(argv[2], &datai);
      printf("output is : %d" , datai);
    } else {
      printf("invalid parameter");
    }
  } else {
    printf("invalid parameter");
  }
  free(data);
  return 0;
}

In this problem, myatoi works fine and the decimal2binary algorithm is correct, but every time I run the code it gives my output as 0. I do not know why. Is it a problem with pointers? I already set the address of variable data but the output still doesn’t change.

./dec2bin "-d" "23" "-b"

Answer 1

The line:

long int fractionfactor = .1;

will set fractionfactor to 0 because the variable is defined as an integer. Try using a float or double instead.

Similarly,

long int dec = myatoi(decimal);

stores an integer value, so wholenum is unnecessary.

---

Instead of

i = (i << 3) + (i<<1) + (*string -'0');

the code will be much more readable as

i = i * 10 + (*string - '0');

and, with today’s optimizing compilers, both versions will likely generate the same object code. In general, especially when your code isn’t working, favor readability over optimization.

---

fraction *= 2;  // times by two first

Comments like this, that simply translate code to English, are unnecessary unless you’re using the language in an unusual way. You can assume the reader is familiar with the language; it’s far more helpful to explain your reasoning instead.