How i convert char array to HEX

Projects Programming
2

If I understand correctly the array contains 2 rows of data, each of 4 characters

Try

for (int row = 0; row < 2; row++)
{
  for (int col = 0; col < 4; col++)
  {
    Serial.print(data_value[row][col]);
  }
}

EDIT : see corrected version in reply #3