How to convert 7.3456788e-12 value to string format for displaying purpose?

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C

string

convert

Hi guys,
I just got stuck with conversion of a big floating value to string format.

In my program,

void double_to_string(long double v)
{
  unsigned char res[40];
  
// here i am using compiler library function sprintf() which will give us the string format
  
  sprintf(res,"%f",v);
  if(strlen(res)>14)
  sprintf(res,"%Le",v);// if the result is having more number of digits
  return(res);

}

void fun1()
{
  long double v;
  unsigned char *result_str;
  v = 0.56726*6.456*1e-12; // based on some calculations i used to get this value
  result_str = double_to_string(v);
  print_result(result_str);
}

When i debug my code, in variable values i found the value of v in double_to_string function like this 3.66223056e-12. But in my sprintf() function giving 0.000000 as result. It's unable to convert such type of value to string. How can i over come this to get the correct results.

Note: My main intention is doing such big calculations and converting them in strings format with more accuracy. (Like our PC calculator)
Due to limitations of my display area, i am choosing exponent results if the resultant string is having more digits.

I hope i mentioned my problem clearly.So, If can any one have solution for this please help me out.Excuse for my poor english.