There is no point simply resending it without getting the format right!

Please, read the instructions on how to post the code and retain the formatting (indenting):
http://www.8052.com/forum/read.phtml?id=82476

It shold then look something like this:

void main()
{
   unsigned char RETURN;
   static char Voltage10[]={'1','2','3','4','5','6','7','8','9'};
   Initial_LCD(); // Run function Initial_LCD
   Init_CPU();    //do all initializations
   while(1)
   {
      RETURN=convert(0);
      LCD_putc( Voltage10(RETURN) );

Is it really?
What about this line:

LCD_putc( Voltage10(RETURN) );

Surely that should be:

LCD_putc( Voltage10[RETURN] );