int a[ 100];

memset( a, 0xFF, sizeof( a));
a[ CONST0] = 0;
a[ CONST1] = 1;
a[ CONST2] = 2;
a[ CONST3] = 3;
...
a[ CONST9] = 9;

const int a[ 100] = { ....}

const int _a[ 10] = { CONST0, CONST1, CONST2, CONST3,.... CONST9}

int convert( int in_data)
{
  int res = -1;
  for( int q = 0; q < ( sizeof( _a) / sizeof( _a[ 0])); q++)
    if( _a[ q] == in_data)
    {
      res = q;
      break;
    }
  return res;
}

const int a[ 100] = {......}

int convert( int in_data)
{
  return a[ in_data];
}

const int a[ 10] = { CONST0, CONST1, CONST2, CONST3,.... CONST9}; // CONST < 100

int coder( int in_data) // in_data < 10
{
  return a[ in_data]; // Out < 100
}

const int b[ 100] = { ...};
int decoder( int in_data)
{
  return b[ in_data];
}

#define SEGMENT_A  0x10
#define SEGMENT_B  0x08
#define SEGMENT_C  0x00
#define SEGMENT_D  0x00
#define SEGMENT_E  0x04

#define CONST0  (SEGMENT_A|SEGMENT_B|SEGMENT_C|SEGMENT_D|SEGMENT_E|SEGMENT_F)

#define SEGMENT_A  0x10
#define SEGMENT_B  0x08
#define SEGMENT_C  0x40
#define SEGMENT_D  0x20
#define SEGMENT_E  0x04
#define SEGMENT_F  0x02
#define SEGMENT_G  0x01

const unsigned char symbols[] = 
{
  SEGMENT_A|SEGMENT_B|SEGMENT_C|SEGMENT_D|SEGMENT_E|SEGMENT_F,
  SEGMENT_B|SEGMENT_C,
  SEGMENT_A|SEGMENT_B|SEGMENT_D|SEGMENT_E|SEGMENT_G,
  SEGMENT_A|SEGMENT_B|SEGMENT_C|SEGMENT_D|SEGMENT_G,
  SEGMENT_B|SEGMENT_C|SEGMENT_F|SEGMENT_G,
  SEGMENT_A|SEGMENT_C|SEGMENT_D|SEGMENT_F|SEGMENT_G,
  SEGMENT_A|SEGMENT_C|SEGMENT_D|SEGMENT_E|SEGMENT_F|SEGMENT_G,
  SEGMENT_A|SEGMENT_B|SEGMENT_C,
  SEGMENT_A|SEGMENT_B|SEGMENT_C|SEGMENT_D|SEGMENT_E|SEGMENT_F|SEGMENT_G,
  SEGMENT_A|SEGMENT_B|SEGMENT_C|SEGMENT_D|SEGMENT_F|SEGMENT_G,
  0,

  SEGMENT_A|SEGMENT_D|SEGMENT_E|SEGMENT_F,            // C
  SEGMENT_B|SEGMENT_C|SEGMENT_E|SEGMENT_F|SEGMENT_G,  //H

  SEGMENT_E|SEGMENT_G,                                //r
};

int get_symbol( unsigned char in_data)
{
  for( int q = 0; q < ( sizeof( symbols) / sizeof( symbols[ 0])); q++)
    if( symbols[ q] == in_data)
    {
      return q;
      break;
    }
  return -1;
}