Adding large integers

[Shisou]

hello everyone,

Well I tried to solve this one on my own but it seems i need your help again :\

I'm trying to write a program to add or subtract two large integers... easy enough..

Where i run into problems is working with pointers. Here's where i'm at right now.

I have a function that takes in the integers as strings and puts it into a struct

//struct declaration
struct integer {
    int* digits;
    int size;
};
//function declaration
struct integer* read_integer(char* stringInt);
 

so far this works fairly well... except when i try to print the digits as integers it gives me the ascii equivilent number (like 54 for 1 or something)

then i have a function to add the two large integers, and this is where i'm currently stuck

// function code
struct integer* add(struct integer *p, struct integer *q){
       int *first, *second, carry, i, length;
       struct integer* final;
       carry = 0;
       if(p[0].size > q[0].size)
          length = p[0].size;
       else
          length = q[0].size;
       for(i=0;i<length;i++){
          if(p[0].digits[i] == "\0"){
             //[WARNING] comparison between pointer and integer
             first = 0;
          else
             *first = p[0].digits[i];
          if(q[0].digits[i] == "\0")
             //[WARNING] comparison between pointer and integer
             second = 0;
          else
             *second = q[0].digits[i];
          final[0].digits[i] = *first + *second + carry;
          if(final[0].digits[i] >= 10){
             final[0].digits[i] = final[0].digits[i] - 10;
             carry = 1;
          }
          else
             carry = 0;
          }
 
}
 

compiling this gives me 2 warning on the lines above comments in code above.
running it will give an access violation and crash the program.

I'm not sure where i'm going wrong but i'm sure it has something to do with my use of pointers.

Any help will be greatly appreciated!

[Laharl]

Using double quotes there means you're comparing it to a string literal. Use single quotes for the character literal you want.

[Shisou]

ahhhh, that got rid of those pesky warnings :) thank you...

however i still get an access violation, and i believe it is at the following line

*first = p[0].digits[i];
 

atleast when i tried to step through this line in my debugger the error popped up :\

[oler1s]

int *first

Why is first a pointer to an int? If you have described a valid reason for it to be a pointer, where does it point?

[Shisou]

I didn't really have a reason for first and second to be pointers... except that it was the only way to get some kind of functionality out of the program... but now that i have the strings converted to integers I think i should be able to use just a regular int.

I'm going to keep working this part alone and see where i can get, if I need anything else I'll be sure to post here again :)

Thanks again!