Decimal to ASCII conversion progam in C

        int hundreds, tens, ones;
	unsigned char buffer[16];
	ones = adc_data%10;
	adc_data = adc_data/10;
	tens = adc_data%10;
	hundreds = adc_data/10;
//Now convert this into ASCII by ORing it with 0x30
ones = ones | 0x30;
tens = tens | 0x30;
hundreds = hundreds | 0x30;

#include<stdio.h>

//create a string variable 
unsigned char buffer[16];

sprintf(buffer,"%d",temp);
//This will convert the temp value to ASCII and these values are stored in buffer..
//don't forget to inculde stdio.h header file.

#include <REGX51.H>
#include<stdio.h>
#include<string.h>

sbit INTR = P3^5;
sbit RD_ADC = P2^4;
sbit WR_ADC = P2^3;
sfr MYDATA = 0x80;        //Port-0
sfr LcdData = 0x90;        //Port-1
sbit RS =  P2^5;
sbit RW =  P2^6;
sbit EN =  P2^7;
void lcdcmd(unsigned char value);
void lcddata(unsigned char value);
void lcdstr(unsigned char msg[]);
void Delay(unsigned int itime);
void SerTX(unsigned char x);
void SerTX_str(unsigned char msg[]);
unsigned char msg[] = "VOLTAGE --->";
void main()
{
    unsigned int temp;
    int hundreds,tens,ones;
    unsigned char buffer[10];
    TMOD = 0x20;    //Timer-1, 8-Bit Auto Reload Mode
    TH1 = 0xFD;        //9600 Baud Rate When Crystal Used is 11.0592MHZ
    SCON = 0x50;
    TR1 = 1;        //Start Timer
    MYDATA = 0xFF;    //Making P1 as Input Port
    INTR = 1;
    RD_ADC = 1;        //Set RD high
    WR_ADC = 1;        //Set WR high
    lcdcmd(0x38);
    Delay(1);
    lcdcmd(0x0E);
    Delay(1);
    lcdcmd(0x01);
    Delay(1);
    lcdcmd(0x80);
    lcdstr("VOLTAGE");
    lcdcmd(0x0C);
    while(1)
    {     
        lcdcmd(0xC0);                                                               
        WR_ADC = 0;        //Send WR Pulse
        Delay(1);
        WR_ADC = 1;        //Low-High Pulse means Start of Conversion
        while(INTR == 1);    //Wait until End of Conversion
        //When Conversion Gets Completed the INTR Pin Goes Low we get out of the Loop
        RD_ADC = 0;        //Send RD Pulse
        temp = MYDATA * 2;
        //Conversion Process Starts Here       
            ones = temp%10;
            temp = temp/10;
            tens = temp%10;
            hundreds = temp/10;
            sprintf(buffer,"%d.%d%d Volts",hundreds,tens,ones);
            lcdstr(buffer);
            SerTX_str(msg);
            SerTX_str(buffer);
            SerTX(13);
            SerTX(13);
            Delay(10);
            Delay(10);
            RD_ADC = 1;
    }
}
void lcdcmd(unsigned char value)
{
    LcdData = value;
    RS = 0;
    RW = 0;
    EN = 1;
    Delay(1);
    EN = 0;
}
void lcddata(unsigned char value)
{
    LcdData = value;
    RS = 1;
    RW = 0;
    EN = 1;
    Delay(1);
    EN = 0;
}
void Delay(unsigned int itime)
{
    unsigned int i,j;
    for(i=0;i<1275;i++)
    for(j=0;j<itime;j++);
}
void lcdstr(unsigned char msg[])
{
    unsigned short int len,i;
    len = strlen(msg);
    for(i=0;i<len;i++)
    {
        lcddata(msg[i]);
        Delay(1);
    }
}
void SerTX(unsigned char x)
{
    SBUF = x;
    while(TI == 0);
    TI = 0;
}
void SerTX_str(unsigned char msg[])
{
    unsigned short len,i;
    len = strlen(msg);
    for(i=0;i<len;i++)
    {   
        SerTX(msg[i]);
    }
}

a[0] = 161/100 = 1
a[1] = 161%100 = 61 , then 61/10 = 6
a[2] = 61%10 = 1

so 

a[0]=0x01
a[1]=0x06
a[2]=0x01

if you add 0x30 to these values then

a[0] | 0x30 =0x31 this is ascii character "1"
a[1] | 0x30 =0x36 this is ascii character "6"
a[2] | 0x30 =0x31 this is ascii character "1"

P2 = 0xff; // from adc 11111111 

temp = P2;

a[0] = temp / 100;

//.......................The rest of the code stays unchanged