how to put an array character into the equation?

i try to put 8 byte character into the equation causing a lot of error,what i'm supposed to do to make sure the equation can take the static value and produce output in the 8 bytes.

#include <math.h>
#include <hidef.h> /* for EnableInterrupts macro */

#include "derivative.h" /* include peripheral declarations */

void voltage_measure(void);

void main(void) {

  voltage_measure();

}

void voltage_measure(void) {
   char Van1[8],VA;
   char Vbn[8],VB;
   char Vcn[8],VC;
   char AC[4],ac;
   char BC[4],bc;
   char AB[4],ab;    
   double Vab1,Vab2,Vbc1,Vbc2,Vac1,Vac2;
   double Vab[8],Vbc[8],Vac[8];

   Van1[0]=0xF0;   
   Van1[1]=0x00;
   Van1[2]=0x00;                                  
   Van1[3]=0x00;

   VA=0x000000F0;

   Vbn[0]=0x78;
   Vbn[1]=0x00;
   Vbn[2]=0x00;
   Vbn[3]=0x00;

   VB=0x78;

   Vcn[0]=0x3C;
   Vcn[1]=0x00;
   Vcn[2]=0x00;
   Vcn[3]=0x00;

   VC=0x3C;

   AB[0]=0xB4;
   AB[1]=0x00;

   ab=0xB4;

   AC[0]=0x2D;
   AC[1]=0x00;

   ac=0x2D;

   BC[0]=0x5A;
   BC[1]=0x00;

   bc=0x5A;
   Vab1=(VB*sin(ab))*(VB*sin(ab))  ;
   Vab2=(VA+(VB*cos(ab)))*(VA+(VB*cos(ab)));
   Vab[4]=sqrt(Vab1+Vab2);

   Vbc1=(VC*sin(bc))*(VC*sin(bc));
   Vbc2=(VB+(VC*cos(bc)))*(VB+(VC*cos(bc))) ;
   Vbc[4]=sqrt(Vbc1+Vbc2);

   Vac1=(VC*sin(ac))*(VC*sin(ac));
   Vac2=(VA+(VC*cos(ac)))*(VA+(VC*cos(ac)));
   Vac[4]=sqrt(Vac1+Vac2);
}

This is what I have understood as yet,

1. you want to do arithmetic with double precision that has several parameters
   • you would like to store the parameters in char variables (maybe to save on space?)
   • I don't know why you try to write VA=0x000000F0; when its a char (1 byte) variable
   • the static value you refer are probably the constants VA etc
   • It might be useful to have all these working in the arithmetic at double precision
   • when you use the sin and sqrt kind of functions, they will work at double anyways
   • you do not have a main function listed here;
   • it would be there in your actual file (that compiles this code)
   • so, i am also assuming you have things like math.h included
     and the math library on the compile command
   • that is, you do get the binary compiled without errors

maybe you can elaborate the problem you are facing a little more?

1. Update from comment 1.
   When you say, "character with 8 byte array" -- are you trying to create a double with an 8 char array?

   • Update from comment 2. If your answer is in double, you can catch it in a double variable.
     A double is already 8-bytes (on most platforms).
     Is there a special reason to get it into a char array or a byte array?

   • Update from comment 3.
     The link error implies you did include a math library for the linking.
     The header just gives function prototypes for compilation.
     With gcc, it would be -lm on the command line.

   • Update from comment 4.
     To convert a double to an integer value check this page,
     How can I convert a floating-point value to an integer in C?