str_num_common.c

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#include <math.h>
#include <string.h>
#include <stdio.h>
 
 
int format_string(char * str)
{
  int i = 0, length = 0, j = 0;
  int sign = 1;
  int flag_dot = 0; // The number of dots in the string should be at most one.
  int pos_dot = 0;
  int flag_e = 0;
  int pos_e = 0;
 
  length = strlen(str);
 
  for(j = 0; j < length; ++j)
  {
    if((str[j] == 69) || (str[j] == 101))
    {
      str[j] = 101;
      flag_e += 1;
      pos_e = j;
    }
  }
 
  // There could not be more than one 'e' in one number.
  if(flag_e > 1)
    return 0;
  if((flag_e) && (pos_e == 0))
    return 0;
  if((flag_e) && (pos_e == length-1))
    return 0;
  // A dot only could not be a number.
  if((str[0] == 46) && (length == 1))
    return 0;
  // A '-' only could not be a number.
  if(str[0] == 45)
  {
    if(length == 1)
      return 0;
    sign = -1;
  }
 
  // Eliminate '-' from the string and return -1.
  if(sign < 0)
  {
    for(i = 0; i < length; ++i) // Eliminate '-'
      str[i] = str[i+1];
    length -= 1;
    pos_e -= 1;
    if(pos_e == 0)
      return 0;
  }
 
  if(flag_e)
  {
    for(i = 0; i < length; ++i)
    {
      if(str[i] == 45)
      {
      // After eliminate '-', the only possible position for '-' is behind 'e'
        if((i-pos_e) != 1)
      return 0;
    else if(i == length-1)
      return 0;
      }
      // There could not be two dots in one number.
      else if((str[i] == 46) && (flag_dot > 0))
        return 0;
      else if(str[i] == 46)
      {
        flag_dot += 1;
        pos_dot = i;
      }
    }
    if((flag_dot) && (pos_dot >= (pos_e-1)))
      return 0;
  }
  else
  {
    for(i = 0; i < length; ++i)
    {
      if(str[i] == 45)
        return 0;
      else if((str[i] == 46) && (flag_dot > 0))
        return 0;
      else if(str[i] == 46)
        flag_dot += 1;
    }
  }
 
  return sign;
}
 
double str2num(char * number)
{
  double result = 0.0, super_script = 0.0;
  int idx = 0, dot = -2;
  int i = 0, j = 0;
  int length = 0;
  int pos_e = 0;
  char * after_e = number;
  int sign = 1;
 
  length = strlen(number);
 
  for(j = 0; j < length; ++j)
    if(number[j] == 101)
      pos_e = j;
 
  if(pos_e)
  {
    after_e = number + pos_e + 1;
    number[pos_e] = 0;
    result = str2num(number);
    if(after_e[0] == 45)
    {
      sign = -1;
      after_e += 1;
    }
    super_script = str2num(after_e);
    result = result * pow(10.0, sign * super_script);
  }
  else
  {
    while(number[idx] != 0)
    {
      if(number[idx] == 46)
      {
        dot = idx - 1;
    idx = 0;
    break;
      }
      ++idx;
    }
 
    if(dot == -2)
      dot = idx - 1;
 
    for (i = 0; i <= dot; ++i)
      result += (double)(number[i] - 48)*pow(10, dot - i);
 
    dot += 1;
    for (i = 1; i < length - dot; ++i)
      result += (double)(number[dot+i] - 48)*pow(0.1, i);
  }
  
  return result;
}