plz explain the code

[apoorvapantoola]

hi actually i have seen this code in a program can any one plz explain me wht is happening in this code......i am new to c programing and i am still learning....


void write_char(char x, char y, char ch, char attb) {
char far * vdu = (char far *)MK_FP(0xb800,00);

*(vdu +(y*160)+(x*2))=ch;
*(vdu +(y*160)+(x*2)+1)=attb;
}

[Henri Korpela]

void write_char(char x, char y, char ch, char attb) {
This is function definition. It defines a function that does not return anything and takes 4 characters as it's parameters (x, y, ch, attb).

char far * vdu = (char far *)MK_FP(0xb800,00);
This statement creates char array/pointer (far is probably a preprocessor definition, hard to tell what it means, it can be const, static, volatile, etc).

Value of this char array/pointer is assigned by function or by preprocessor definition MK_FP, which takes in one char value & one int value, first value represented in hexadecimals & second value as an ordinary number in decimals. The result of MK_FP is then converted into char array/pointer with C-style type cast.

*(vdu +(y*160)+(x*2))=ch;
*(vdu +(y*160)+(x*2)+1)=attb;
}

Even though x & y are both characters (char), it is possible to make arithmetic operations (+ & *) with them. After all, they are like ints, but with smaller range (-128 - 128 or 0 - 255 if dealing with unsigned chars). In this statement, the address of vdu is increased by the value of y multiplied by 160, which is increased x multiplied by 2. Then, ch is assigned to address of address of vdu. The following statement is very similiar, it does almost the same thing with minor differences.

If you didn't understand what I told you (I explained the best I could), then I recommend you to learn more C before going to advanced level like this. I admit, my explanation is not the most beginner-friendly, but I hope it is useful. If you want to ask me something, please feel free to do so.

[apoorvapantoola]

Thq very much.......i understood what u explained....thx a lot for helping me out.....

[bluecoder]

one more quick question , Why is far pointer used ?