need help on message display program

[vead]

Hello
I have written this program to display the numbers on screen

---

Code C - [expand]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
#include<reg51.h>
#define display_port P1      //Data pins connected to port 2 on microcontroller
sbit rs = P2^0;  //RS pin connected to pin 2 of port 3
sbit rw = P2^1;  // RW pin connected to pin 3 of port 3
sbit e =  P2^2;  //E pin connected to pin 4 of port 3
 
void main()
{
    unsigned int number[15]="012345";  .
    int l=0;
    lcd_init();
    while(number[l] != '\0')
    {
        lcd_data(number[l]);
        l++;
        msdelay(50);
    }
}
 
void msdelay(unsigned int time)  // Function for creating delay in milliseconds.
{
    unsigned i,j ;
    for(i=0;i<time;i++)    
    for(j=0;j<1275;j++);
}
void lcd_cmd(unsigned char command)  //Function to send command instruction to LCD
{
    display_port = command;
    rs= 0;
    rw=0;
    e=1;
    msdelay(1);
    e=0;
}
 
void lcd_data(unsigned char disp_data)  //Function to send display data to LCD
{
    display_port = disp_data;
    rs= 1;
    rw=0;
    e=1;
    msdelay(1);
    e=0;
}
 
 void lcd_init()    //Function to prepare the LCD  and get it ready
{
    lcd_cmd(0x38);  // for using 2 lines and 5X7 matrix of LCD
    msdelay(10);
    lcd_cmd(0x0c);  // turn display ON, cursor blinking 
    msdelay(10);
    lcd_cmd(0x01);  //clear screen
    msdelay(10);
    lcd_cmd(0x81);  // bring cursor to position 1 of line 1
    msdelay(10);
}

---

I don't understand this part of program. I don't understand what does program do in main function

---

Code C - [expand]
1
2
3
4
5
6
7
8
9
10
11
12
void main()
{
    unsigned int number[15]="012345";  
    int l=0;
    lcd_init();
    while(number[l] != '\0')
    {
        lcd_data(number[l]);
        l++;
        msdelay(50);
    }
}

---

arrays are declared and initialize in the following form

unsigned int number[15]="012345";

I understand what is array

number[0] =  0
number[1]=  1
number[2] = 2
number[3] = 3
number[5] = 4
number[6] = 5
number[7]
number[8]
number[9]
number[10]
number[11]
number[12]
number[13]
number[14]
number[15]

I don't understand how does program work in main function. what is meaning of this line lcd_data(number[l]);?

 

[betwixt]

void main() the function name
{
unsigned int number[15]="012345"; declare and initialize the array (note: could be char size instead of int)
int l=0; l is used as an index into the array
lcd_init(); configure the LCD so its ready to display things
while(number[l] != '\0') repeat the following until the end of string (end of array) is found
{
lcd_data(number[l]); display the array value indexed by l
l++; increment the index so it points to the next value in the array
msdelay(50); just a delay, presumably to allow the LCD time to display the character
}
}

Note that there is a serious flaw in the code. It assumes the final value in the array is zero. In 'C' a string is stored with a zero terminator at the end but because you load the values 'manually' in the array it may not be there and the LCD could try to continue displaying garbage until it finds a zero from somewhere else or 'l' overflows back to zero.
You can fix that in one of two ways, either make the last value in your array a zero (/0 rather than character zero) or you can declare the array as a character string instead of unsigned integers.

Brian.

 

[hexreader]

I think vead is trying to make the following (corrected) statement:

Arrays can be declared and initialised in the following way:

unsigned char number[15] = "012345";          // assign a text buffer and fill the first 7 elements with 6 ASCII characters and a null terminator of zero

The C compiler will automatically add a null terminator if a string is declared this way.

This results in the following array:

number[0] = 0x30;     // ASCII for '0'
number[1] = 0x31;     // ASCII for '1'
number[2] = 0x32;     // ASCII for '2'
number[3] = 0x33;     // ASCII for '3'
number[5] = 0x34;     // ASCII for '4'
number[6] = 0x35;     // ASCII for '5'
number[7] = 0x00;     // null terminator of zero
number[8]                  // rest of array unknown, as not initialised 
number[9]
number[10]
number[11]
number[12]
number[13]
number[14]
number[15]

 

[vead]

I am confused on only two statement
1. while(number[l] != '\0')
2. lcd_data(number[l]);

what is number[l]) here number is name of variable what is [l]) ?

 

[hexreader]

1. while(number[l] != '\0')

This is exactly the same as:

while(number[l] != 0) // loop through ASCII characters until terminator of zero is found

since '\0' is just a fancy way of indicating the number zero, but in ASCII character style.

2. lcd_data(number[l]);

this calls function lcd_data with a byte of data as the parameter given to the function.

number[l] is a byte of data (or an int of data if we take your original code). it fetches 0x30 on the first loop iteration where l is zero (because you initialised it to zero earlier), since number[0] contains 0x30
Since l is incremented each loop, successive ASCII characters are retrieved from array number[] until a zero is found