Help on arrays

[alvin_aldrich]

hi everyone,

I would just like to ask what (long)table_1 means? The table_1 is defined below. I do get a value of 4395176 with this code

printf("table 1 is %d\n", table_1);

But i dont know what operation was done? Can someone please help

unsigned char table_1[256] = {
0x08, 0xCB, 0x54, 0xCF, 0x97, 0x53, 0x59, 0xF1,
0x66, 0xEC, 0xDB, 0x1B, 0xB1, 0xE2, 0x36, 0xEB,
0xB3, 0x8F, 0x71, 0xA8, 0x90, 0x7D, 0xDA, 0xDC,
0x2C, 0x2F, 0xE8, 0x6A, 0x73, 0x37, 0xAE, 0xCC,
0xA1, 0x16, 0xE6, 0xFC, 0x9C, 0xA9, 0x2A, 0x3F,
0x58, 0xFD, 0x56, 0x4C, 0xA5, 0xF2, 0x33, 0x99,
0x1A, 0xB7, 0xFE, 0xA6, 0x1E, 0x32, 0x9E, 0x48,
0x03, 0x4A, 0x78, 0xEE, 0xCA, 0xC3, 0x88, 0x7A,
0xAC, 0x23, 0xAA, 0xBD, 0xDE, 0xD3, 0x67, 0x43,
0xFF, 0x64, 0x8A, 0xF9, 0x04, 0xD0, 0x7B, 0xC2,
0xBC, 0xF3, 0x89, 0x0E, 0xDD, 0xAB, 0x9D, 0x84,
0x5A, 0x62, 0x7F, 0x6D, 0x82, 0x68, 0xA3, 0xED,
0x2E, 0x07, 0x41, 0xEF, 0x2D, 0x70, 0x4F, 0x69,
0x8E, 0xE7, 0x0F, 0x11, 0x19, 0xAF, 0x31, 0xFB,
0x8D, 0x4B, 0x5F, 0x96, 0x75, 0x42, 0x6C, 0x46,
0xE4, 0x55, 0xD6, 0x3B, 0xE1, 0xD1, 0xB0, 0xB5,
0x45, 0x29, 0xC0, 0x94, 0x9F, 0xD4, 0x15, 0x17,
0x3C, 0x47, 0xC8, 0xD9, 0xC6, 0x76, 0xB9, 0x02,
0xE0, 0xC9, 0xB2, 0x01, 0xC1, 0x5D, 0x4E, 0x14,
0xF4, 0xAD, 0xB6, 0x00, 0x72, 0xF0, 0x49, 0x0D,
0xD8, 0x5E, 0x6F, 0x2B, 0x8C, 0x51, 0x83, 0xC5,
0x0A, 0x85, 0xE5, 0x38, 0x7E, 0x26, 0xEA, 0x22,
0x6B, 0x06, 0xD5, 0x8B, 0xBF, 0xC7, 0x35, 0x1D,
0xF6, 0x24, 0x28, 0xCE, 0x9B, 0x77, 0x20, 0x60,
0xF5, 0x87, 0x3D, 0x65, 0x86, 0x0C, 0xDF, 0xBA,
0x12, 0xA4, 0x3A, 0x34, 0xD7, 0xA0, 0xF8, 0x63,
0x52, 0x27, 0xB8, 0x18, 0xA7, 0x13, 0x91, 0x09,
0x93, 0x5C, 0x10, 0x9A, 0xB4, 0xE9, 0x44, 0xC4,
0x21, 0x57, 0x1C, 0x0B, 0xA2, 0x74, 0x4D, 0xBE,
0xD2, 0x1F, 0xCD, 0xE3, 0x6E, 0x7C, 0x40, 0x50,
0x39, 0x80, 0x98, 0xFA, 0x25, 0x92, 0x30, 0x5B,
0x05, 0x95, 0xBB, 0x79, 0x61, 0x3E, 0x81, 0xF7 };

[Ancient Dragon]

>>printf("table 1 is %d\n", table_1);

That only prints the memory address of the beginning of table_1, which is an array of binary data. I have no idea what is stored in that array, you might get an idea from the program that contains the array.

[hollystyles]

Take the first item in the array 0x08

we know from the 0x it's a hexidecimal number (base 8) 0x is how you identify a hexidecimal number the 08 represents the number in decimal thats 8 in binary it's 00001000 (I won't go into how to convert between binary and hex and decimal you can Google that)

So what you've got is a list of 256 numbers.

Now table_1 is a pointer to the start of the array of numbers in RAM
%d tells printf to interpret the second argument as an integer.
so the program prints the RAM address of the start of the array table_1 is pointing to as an integer .

Everything is numbers to a computer, but they can be interpreted in many ways, to represent charcters from the alphabet or matmatical symbols or pitch and tone through a sound card.

all 'char' is to the computer is 8 bits 00000000 or 1 byte, it doesn't mean there is a charcter in it that you and I would recognise.

If you do

printf("%s", table_1);

With %s instead of %d to tell printf to interpret table_1 as a string of chars, you will get a load of garbage on screen.

[alvin_aldrich]

Wow. Thanks for the fast reply. Ok i get it now.

Really appreciate the help

:D

[Dave Sinkula]

Take the first item in the array 0x08

we know from the 0x it's a hexidecimal number (base 8)

Hexadecimal is base 16 -- octal (base 8) has a leading zero, but not x or X.

Now table_1 is a pointer to the start of the array of numbers in RAM

It's not a pointer, it's an array. But when used in an expression it is implicitly converted to a pointer to the first element.

all 'char' is to the computer is 8 bits 00000000 or 1 byte, it doesn't mean there is a charcter in it that you and I would recognise.

A char is not necessarily 8 bits, that is merely a minimun. But very frequently a byte, the space required to hold a char, is 8 bits.

[hollystyles]

Drat, just when you think you know something, it turns out you don't know squat.

I did know hexidecimal was base 16, luckily I don't have to deal with it on a daily basis so I guess I'm losing the edge, sob....