result is not written to adc register because it has been locked.

// LCD module connections

sbit LCD_RS at PORTD0_bit;

sbit LCD_EN at PORTD1_bit;

sbit LCD_D4 at PORTD2_bit;

sbit LCD_D5 at PORTD3_bit;

sbit LCD_D6 at PORTD4_bit;

sbit LCD_D7 at PORTD5_bit;


sbit LCD_RS_Direction at DDD0_bit;

sbit LCD_EN_Direction at DDD1_bit;

sbit LCD_D4_Direction at DDD2_bit;

sbit LCD_D5_Direction at DDD3_bit;

sbit LCD_D6_Direction at DDD4_bit;

sbit LCD_D7_Direction at DDD5_bit;

// End LCD module connections


unsigned int ADC = 0,adc_result=0;

unsigned char display[7];



void main() {
   
    Lcd_Init(); // Initialize LCD
   
    Lcd_Cmd(_LCD_CLEAR); // Clear display
   
    Lcd_Cmd(_LCD_CURSOR_OFF); // Cursor off
   
   
    Lcd_Out(1,1,"ADC:"); // Write text in first row
   
   
    ADIE_bit = 1;
   
    ADEN_bit = 1;
   
    ADFR_bit = 0;
   
    ADIF_bit = 0;
   
    ADPS2_bit = 1;
   
    ADPS1_bit = 1;
   
    ADPS0_bit = 1;
   
   
   
    ADMUX = 0b01000000;
   
    while(1){
       
        //ADIE_bit = 1;
       
        ADSC_bit = 1;
       
        while(!ADIF_bit);
       
        ADIF_bit = 0;
       
        ADC = (ADCH * 256) + ADCL;
       
        IntToStr(ADC,display);
       
        Lcd_Out(2,1,display);
       
    }
   
}

// LCD module connections
sbit LCD_RS at PORTD0_bit;
sbit LCD_EN at PORTD1_bit;
sbit LCD_D4 at PORTD2_bit;
sbit LCD_D5 at PORTD3_bit;
sbit LCD_D6 at PORTD4_bit;
sbit LCD_D7 at PORTD5_bit;

sbit LCD_RS_Direction at DDD0_bit;
sbit LCD_EN_Direction at DDD1_bit;
sbit LCD_D4_Direction at DDD2_bit;
sbit LCD_D5_Direction at DDD3_bit;
sbit LCD_D6_Direction at DDD4_bit;
sbit LCD_D7_Direction at DDD5_bit;
// End LCD module connections

unsigned int ADC = 0,adc_result=0;
unsigned char display[7];


void main() {
  Lcd_Init();                        // Initialize LCD
  Lcd_Cmd(_LCD_CLEAR);               // Clear display
  Lcd_Cmd(_LCD_CURSOR_OFF);          // Cursor off

  Lcd_Out(1,1,"ADC:");                 // Write text in first row

       ADIE_bit = 1;
       ADEN_bit = 1;
       ADFR_bit = 0;
       ADIF_bit = 0;
       ADPS2_bit = 1;
       ADPS1_bit = 1;
       ADPS0_bit = 1;

       ADMUX = 0b01000000;
       DDRC.F0 = 0;

       while(1){
            ADSC_bit = 1;
        while(!ADIF_bit);
        ADIF_bit = 0;
        ADC = (ADCH * 256) + ADCL;
            IntToStr(ADC,display);
            Lcd_Out(2,1,display);
       }
}

/* Safe way to read ADC result register */
adc_result = ADCL; /* Read the low byte */
adc_result += (ADCH<<8); /* Read and add the high byte */