Question

I’ve wrote a program that gets a string, and then calculate a total value of the string togheder…
For Example :

char data[256] = "1$0.83331333333333334$false$false"; // the data

Here I need to do the calculation of 1 + 0.83331333333333334
so this is what I wrote:

char data[256] = "1$0.83331333333333334$false$false"; // the data
double grade = 0;
int i = 0;
int times = 0;
char temp[256] = "";

int flag = 0;

while (flag == 0)
{
      times = 0;

      if (isdigit(data[i])) // if it's a number
      {
                           if (data[i + 1] == '.') // if it's a double number
                           {
                                      i = i + 2;
                              while (isdigit(data[i])) // putting it into a temp array
                              {
                                  temp[i] = data[i];
                                  i++;
                                  times++;
                              }
                              grade = grade + (double)temp / (times * 10);
                           }
                           grade = grade + (int)data[i]; // if it's an int number, putting it into grade right away
      }

      if (data[i] == '\0')
      {
                  flag = 1;
      }

      i++;
}

printf ("%f\n", grade);

the problem is in the line :

grade = grade + (double)temp / (times * 10);

it says “pointer value used where a floating point value was expected”.
I really couldent understand whats the problem…

Thanks 🙂

Edit:

Thanks for your help!
I’ve been able to convert the number into a string..
so for example, now if I have the big string in data, with couple of doubles inside it, I can take in a loop every time the double into a new string.
I’ve used atof to convert it into a double, though it seems that the double is too small..
For example :
I have in the string temp : “83331333333333334”, and I used atof on it -> the new double has 8333313 only… the rest is like not going into the double..
I guess that the number is too big for a double number… so what Can I do ?
Thanks!

Answer 1

You cannot simply cast a char array to double and expect the compiler to treat it as a double. You need to convert temp via a suitable function such as strtod and then use that value in your calculations.

Note that strod requires a C-style string i.e. null-terminated character array. So, passing in temp is not enough. You need to null terminate temp i.e. once you are done inserting the digits, add an temp[ i ] = 0;.

Here’s a little program that will probably help you fix your errors and help you use strtod:

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

int main() {
 char data[256] = "1$0.83331333333333334$false$false"; // the data
 char *p = strtok( &data[ 0 ], "$" ); 
 while (p) {
    double d = strtod( p, NULL );
    printf( "extracted value = %.10f\n", d );
    p = strtok( NULL, "$" );
 }
}

Since the OP wanted something simpler than strtod:

You can use double atof(const char *nptr);. In my sample source replace the strtod( p, NULL ); by atof( p ); and that should get you started. The problem with atof and friends is that error handling is difficult and if the value cannot be represented you silently invoke undefined behavior.