Assignment HELP!!

I need help with this assignment, any takers? I need to fill in the functions and make it work

Computer Science

The Problem
The unsigned int type in C requires 4 bytes of memory storage. With 4 bytes we can store integers as large as 232-1; but what if we need bigger integers, for example ones having hundreds of digits? If we want to do arithmetic with such very large numbers we cannot simply use the unsigned data type. One way of dealing with this is to use a different storage structure for integers, such as an array of digits. If we represent an integer as an array of digits, where each digit is stored in a different array index. Since the integers are allowed to be as large as we like, a dynamically-sized array will prevent the possibility of overflows in representation. However we need new functions to add, subtract, compare, read and write these very large integers.

175—way to store in array index 0=5 1=7 2=1
Doing this all major operations goes from least sig digit to most significant digit.S
Write several functioms

Write a program that will manipulate such arbitrarily large integers. Each integer should be represented as an array of digits, where the least significant digit is stored in index 0. Your program should be able to read in a string of digits and create a struct that stores the big integer.

Your program should store each decimal digit (0-9) in a separate array element. In order to perform addition and subtraction more easily, it is better to store the digits in the array in the reverse order. For instance, the value 1234567890 would be stored as:

index 0 1 2 3 4 5 6 7 8 9
array 0 9 8 7 6 5 4 3 2 1

Note: Although this seems counter-intuitive, it makes the code slightly easier, because in all standard mathematical operations, we start with the least significant digits. It also makes sense that the digit at the place 10i is stored in index i.

Your program should include the following functions:

• a function that will read in an integer from the keyboard-read into string and convert digit by digit
• a function that will print an integer.
• a function that will add two integers and return the result.
• a function that compares two integers and returns -1 if the first is less than the second, 0 if they are equal, and 1 if the first is greater than the second.
• a function that will subtract one integer from the other and return the result. Since you’ll be dealing with positive integers only, the result should be a positive number. To ensure that the result is integer you should subtract the smaller number from the larger one. If they are equal, 0 should be returned.this will always return a non negative result. Return pos6 not neg 6 . there are prototypes.
Input/Output Specification
Your program should allow the user to do two things:

1) Add two big integers
2) Subtract to big integers

Instead of getting input from the user, you read in input from a file, "bigint.txt". (This will expedite the grading process.)

The input file format is as follows:

The first line will contain a single positive integer, n, representing the number of operations to carry out. The next n lines will contain one problem each. Each line will have three integers separated by white space. The first integer on each of these lines is guaranteed to either be 1 or 2, indicating addition and subtraction, respectively. The next two integers on the line will be the two operands for the problem. You may assume that these two integers are non-negative, are written with no leading zeros (unless the number itself is 0) and that the number of digits in either of the numbers will never exceed 200.

You should generate your output to the screen. In particular, you should generate one line of output per each input case. Your output should fit one of the two following formats:

X + Y = Z
X – Y = Z

corresponding to which option was chosen. For the first option, always print the first operand first. For the second option, always print the larger of the two operands first. If the two operands are equal, the same number is printed both times.

Implementation Restrictions
You must use the following struct:

Code:

---

struct integer {
        int* digits;
        int size;
}

---

Whenever you store or return a big integer, always make sure not to return it with any leading zeros. Namely, make sure that the value stored in index size-1 is NOT zero. The only exception to this rule is if 0 is being stored. 0 should be stored in an array of size 1.


Here are the prototypes of the functions for you to write:

//Preconditions: the first parameter is string that stores
// only contains digits, doesn't start with
// 0, and is 200 or fewer characters long.
//Postconditions: The function will read the digits of the
// large integer character by character,
// convert them into integers and return a
// pointer to the appropriate struct integer.
struct integer* read_integer(char* stringInt);

//Preconditions: p is a pointer to a big integer.
//Postconditions: The big integer pointed to by p is
// printed out.
void print(struct integer *p);

//Preconditions: p and q are pointers to struct integers.
//Postconditions: A new struct integer is created that
// stores the sum of the integers pointed to
// by p and q and a pointer to it is
// returned.
struct integer* add(struct integer *p, struct integer *q);

//Preconditions: p and q are pointers to struct integers.
//Postconditions: A new struct integer is created that
// stores the absolute value of the
// difference between the two and a pointer
// to this is returned.
struct integer* subtract(struct integer *p, struct integer *q);

//Preconditions: Both parameters of the function are
// pointers to struct integer.
//Postconditions: The function compares the digits of two
// numbers and returns:
// -1 if the first number is smaller than the second,
// 0 if the first number is equal to the second number,
// 1 if the first number is greater than the second.
int compare(struct integer *p, struct integer *q);

Sample Input File
3
1 8888888888 2222222222 take8888.. plus 222..
2 9999999999 10000000000
2 10000000000 9999999999

Corresponding Output
8888888888 + 2222222222 = 11111111110
10000000000 – 9999999999 = 1 have to flip around
10000000000 – 9999999999 = 1

[Here we have some stuff without code tags since I too would rather not scroll endlessly right or bother to break lines if I am going to use code tags, since the point of code tags is to escape formatting such as enforced line length! Since we are are computer programming, let's not ignore TOO MUCH the actual computer and all.]


I need help with this assignment, any takers? I need to fill in the functions and make it work

Computer Science

The Problem
The unsigned int type in C requires 4 bytes of memory storage. With 4 bytes we can store integers as large as 232-1; but what if we need bigger integers, for example ones having hundreds of digits? If we want to do arithmetic with such very large numbers we cannot simply use the unsigned data type. One way of dealing with this is to use a different storage structure for integers, such as an array of digits. If we represent an integer as an array of digits, where each digit is stored in a different array index. Since the integers are allowed to be as large as we like, a dynamically-sized array will prevent the possibility of overflows in representation. However we need new functions to add, subtract, compare, read and write these very large integers.

175—way to store in array index 0=5 1=7 2=1
Doing this all major operations goes from least sig digit to most significant digit.S
Write several functioms

Write a program that will manipulate such arbitrarily large integers. Each integer should be represented as an array of digits, where the least significant digit is stored in index 0. Your program should be able to read in a string of digits and create a struct that stores the big integer.

Your program should store each decimal digit (0-9) in a separate array element. In order to perform addition and subtraction more easily, it is better to store the digits in the array in the reverse order. For instance, the value 1234567890 would be stored as:

index 0 1 2 3 4 5 6 7 8 9
array 0 9 8 7 6 5 4 3 2 1

Note: Although this seems counter-intuitive, it makes the code slightly easier, because in all standard mathematical operations, we start with the least significant digits. It also makes sense that the digit at the place 10i is stored in index i.

Your program should include the following functions:

• a function that will read in an integer from the keyboard-read into string and convert digit by digit
• a function that will print an integer.
• a function that will add two integers and return the result.
• a function that compares two integers and returns -1 if the first is less than the second, 0 if they are equal, and 1 if the first is greater than the second.
• a function that will subtract one integer from the other and return the result. Since you’ll be dealing with positive integers only, the result should be a positive number. To ensure that the result is integer you should subtract the smaller number from the larger one. If they are equal, 0 should be returned.this will always return a non negative result. Return pos6 not neg 6 . there are prototypes.
Input/Output Specification
Your program should allow the user to do two things:

1) Add two big integers
2) Subtract to big integers

Instead of getting input from the user, you read in input from a file, "bigint.txt". (This will expedite the grading process.)

The input file format is as follows:

The first line will contain a single positive integer, n, representing the number of operations to carry out. The next n lines will contain one problem each. Each line will have three integers separated by white space. The first integer on each of these lines is guaranteed to either be 1 or 2, indicating addition and subtraction, respectively. The next two integers on the line will be the two operands for the problem. You may assume that these two integers are non-negative, are written with no leading zeros (unless the number itself is 0) and that the number of digits in either of the numbers will never exceed 200.

This is an interesting assignment because of the tip about storing the numbers backwards because of the "least significant digit" being the most processed in arithmetic. I think the prof is being a bit picky with the struct tho, because really you could use array[0] for the size and skip a struct completely which also makes the coding easier. Loops, loop, loops.

I'm not going to do it anyway, tho. I would say from the list beginning with "Your program should include the following functions" the first two are obviously the easiest so begin there, probably with the first one (input), but keeping in mind you must deal with the second one (output).

Quote:

---

Originally Posted by MK27

.

---

Wow MK u sure did have time to reply to this post, sure was a lot!

Wire $1,000,000 non-sequential US dollars to an off shore account of my choosing.
PM me when you have the money ready and I will give you further instructions from there.

Read our forum's homework policy, please! We don't *do* your homework for you. We will try to help you, if you will post your code /pseudo code, and explain your problem accurately and concisely.

I'm not even going to take the time to read some long-winded assignment paper. That's your job.

If you aren't willing to work on your assignment, I'm certainly not going to.

The assignment is well specified, and it sounds easy enough. So my questions to you:
Are there any bits you don't understand that we can clarify for you?
Where is your code? We can't help until you've made a start on it and have gotten stuck.
Even if you have no clue how to implement the algorithms asked of you, you can make a compile-able program by starting with add and subtract functions that just return 0 initially.

I'm having trouble where to start off.. i need to read in the strings into a character array and then convert it to integers with the strtok function. This is what i have..

Code:

---

struct integer* read_integer(char* stringInt)
{
    char* stringInt;
    int size;
    char delims [] = " \n";
    int line[MAXLEN];
    int i;
   
    FILE *fin;
    fin = fopen("bigint.txt","r"); // Open the file for reading
    fscanf(fin, "%d", &size); //Read in how many lines there are
   
    //Allocate memory for the struct with malloc
    integer = (struct integer*)(malloc(size*sizeof(struct integer*)));
   
    //Check to see if malloc is Null, if so crash program.
    if(integer = (struct integer*)(malloc(size*sizeof(struct integer*)))== NULL);
    {
        printf("Malloc Failed\n");
        return 0;
    }
   
    fgets(line, MAXLEN, fin);
   
    for(i = 0; i < size; i++)
    {
        fgets(line, MAXLEN, fin);// read in second line of file?
        strtok(line, delims);// Set up string tokenizer to split the string up based on the limits
        stringInt = (char*)strtok(NULL, delims);
        integer[i].choice = atoi(stringInt);
       
        stringInt = (char*)strtok(NULL, delims);
        integer[i].digits = atoi(stringInt);
       
        stringInt = (char*)strtok(NULL, delims);
        integer[i].size; = atoi(stringInt);
    }
   
   
    // Clean up Function
    free(integer);
    fclose(fin);
    return struct integer;
}

---

Code:

---

integer = (struct integer*)(malloc(size*sizeof(struct integer*)));

---

1. do not cast malloc - read FAQ
2. you allocating space for size pointers not size structs
3.

Code:

---

    if(integer = (struct integer*)(malloc(size*sizeof(struct integer*)))== NULL);

---

result of the previous malloc is lost
Should be

Code:

---

if(integer == NULL)

---

Do not forget to check the return value of fgets

Second line of the file is just ignored?

Code:

---

struct integer* read_integer(char* stringInt)
{
    char* stringInt;

---

Why do you need two of them?

Code:

---

    free(integer);
    fclose(fin);
    return struct integer;

---

you should return variable - not type
you should not free memory, if you plan return pointer to this memory

Since the specifications include this: "a function that will read in an integer from the keyboard-read into string and convert digit by digit" but of course you may also want to read from a file, I would write a "read_integer" function that could do both by accepting a FILE* as a parameter (keyboard input is FILE *stdin and it already exists). Look:

Code:

---

#include <stdio.h>

int read_integer (FILE *in, char *stringint) {
        int i=0, ch;
        while ((ch=fgetc(in))>0) {
                if (ch=='\n') break;
                stringint[i]=ch;
                i++;
        }
        stringint[i]='\0';
        return i;
}
       

int main () {
        char buffer[200];
        int len=read_integer(stdin, buffer);
        printf("%s length=%d\n", buffer, len);
}

---

This does not reverse the numbers or put them into a struct, but it does return the number of digits in the string. Plus you can read numbers from a file:

Code:

---

FILE *fp=fopen("some.file", "r");
len=read_integer(fp, buffer);

---

Some output from the first example:
[root~/C] ./a.out
12347198234501238411324512345
12347198234501238411324512345 length=29

Code:

---

char ch;
        while ((ch=fgetc(in))>0)

---

fgetc returns int, so using char to store the result even before you are sure it could be stored there -just asking for troubles.
On compiler where char is unsigned - you'll be unable to determine the EOF condition
On compilers where char is signed - you'll be unable to read chars from the 128-255 range

Quote:

---

Originally Posted by vart

fgetc returns int, so using char to store the result even before you are sure it could be stored there -just asking for troubles.
On compiler where char is unsigned - you'll be unable to determine the EOF condition

---

Yes, very true, I will change this in the previous post!

how do i read the string in using fscanf ?
how do i pass my char array to the first function if i have it in main.

Code:

---

# include<stdio.h>

int main(void)
{
  # include<stdio.h>

int main(void)
{
    int numlines;
    char stringline[200];
   
    FILE *fin;
    fin = fopen("bigint.txt","r");
    fscanf(fin, "%d", &numlines); //Read in how many lines there are
    fscanf(fin, "%s", &stringline);
    printf("stringline = %d\n", stringline);
    printf("%d\n", numlines);
   
    fclose(fin);
    system("PAUSE");
    return 0;
}

}

---

fscanf(fin, "%s", &stringline);
you do not need & here

printf("stringline = %d\n", stringline);
format is wrong

Cannot get the function to add my numbers..

Code:

---

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAXLEN 200
   
struct integer* read_integer(char* stringInt);
void print(struct integer *p);
struct integer* add(struct integer *p, struct integer *q);
struct integer* subtract(struct integer *p, struct integer *q);
int compare(struct integer *p, struct integer *q);

struct integer{
    int *digits;
    int size;
};

int main(void){
    int numlines; //Number of lines stored in the file
    char string1[200];
    char string2[200];
    int i;// loop index
    int opr; //Operator 1 or 2 tells us if we add or subtract
    struct integer *p;
    struct integer *q;

    // Open the file and read from bigint.txt
    FILE *fin;
    fin = fopen("bigint.txt","r");
    fscanf(fin, "%d", &numlines); //Read in how many lines there are in the file

    // read a line (\n)
    // read the operator(1 or 2) - forget about this one. 3 fscanf
    //scanf first sting; call read int (1st) function
    //same with the second string
    //if 1 then call add, if 2 then call subtract
    // end of loop
    for(i = 0; i < numlines; i++)
    {
        fscanf(fin, "%d", &opr);  // find out whether its add or subtract
        fscanf(fin, "%s", string1); // scan in 2nd number on the first line of input file
            p = read_integer(string1);
        fscanf(fin, "%s", string2);// scan in 3rd number on the first line of input file
            q = read_integer(string2);
   
        printf(string1);//call function to print out information
        printf("\n");
        printf(string2);
        printf("\n");

        if(opr == 1)
        {
         
        // add
        }
        else if(opr == 2)
        {
        // subtract func 
        }
    }
   

       
    fclose(fin);
    system("PAUSE");
    return 0;
}

//Preconditions: the first parameter is string that stores
//              only contains digits, doesn't start with
//              0, and is 200 or fewer characters long.
//Postconditions: The function will read the digits of the
//        large integer character by character,
//        convert them into integers and return a
//            pointer to the appropriate struct integer.
struct integer* read_integer(char* stringInt)
{
    int len;
    struct integer *myString;//create a new struct
    int i;//loop index
    //allocate memory for the struct
    myString = (struct integer*)(malloc(sizeof(struct integer)));
   
    len = strlen(stringInt); // length of the strinInt in digits
   
    myString->size = len; // length of string assigned to size in struct myString
   
    //allocate memory for digits
    myString->digits = (int*)(malloc(sizeof(int)* len));
   
    // assign number to digits, convert to integers
    for(i = 0; i < len; i++)
    {
        myString->digits[i] = stringInt [len-1-i] - '0';
    }
    return myString;
}

//Preconditions: p is a pointer to a big integer.
//Postconditions: The big integer pointed to by p is
//                printed out.
void print(struct integer *p)
{
//given pointer, want to print out digits in reverse order...
    int i;
    // no reversing in add or subtract, but want to reverse here
    for(i = p->size-1; i >= 0; i--)
    {
        printf("%d\n", p->digits[i]);
    }
   
}
//Preconditions: p and q are pointers to struct integers.
//Postconditions: A new struct integer is created that
//                stores the sum of the integers pointed to
//                by p and q and a pointer to it is
//                returned.
struct integer* add(struct integer *p, struct integer *q)
{
    int i;
    struct integer *addAnsw; //create new struct for answer
   
    //Allocate memory for the new struct
    addAnsw = (struct integer*)(malloc(sizeof(struct integer)));
   
    if(p->size > q->size)
    {
        addAnsw = (int*)(malloc(sizeof(int)*(p->size)));
    }
    for(i ; i; i++)
    {
    addAnsw = p->digits[i] + q->digits[i];
    }
   
    return addAnsw;
}

---

Quote:

---

Originally Posted by cprogrammer22

Cannot get the function to add my numbers..

---

So at some point you learned to add, right? If I give you

Code:

---

  198465412
+ 2376418749
  ----------

---

how do you add numbers together?

yeah i know how to add im having trouble with the function, im not gettin the numbers added when i call it and not sure if i use a for loop or what?

Somethings very fishy here!

Your functions name is "print", but you call something called "printf()":

Code:

---

        printf(string1);//call function to print out information

---

which should have given you a compiler error a mile wide!

If you aren't receiving compiler errors, you need to fix that with your compiler. If you *are* receiving compiler errors, you need to pay attention to them.

Fix this, and post up a sample of your input and output, please, so we're all on the same page here.

Quote:

---

Originally Posted by Adak

Somethings very fishy here!

Your functions name is "print", but you call something called "printf()":

Code:

---

        printf(string1);//call function to print out information

---

which should have given you a compiler error a mile wide!

If you aren't receiving compiler errors, you need to fix that with your compiler. If you *are* receiving compiler errors, you need to pay attention to them.

Fix this, and post up a sample of your input and output, please, so we're all on the same page here.

---

What reason do you see to get a compiler error here?
first parameter of printf is format - const char*

string1 is char*

other parameters are optional.

So what could compiler complain here about?

Quote:

---

Originally Posted by cprogrammer22

yeah i know how to add im having trouble with the function, im not gettin the numbers added when i call it and not sure if i use a for loop or what?

---

So write down on a piece of paper how you would add numbers together. Look for patterns that can be abstracted into a loop. Figure out where you have to start and where you have to stop (not as trivial as it sounds, I would bet).

It looked to me like he meant to call his own function "print", but misspelled it as printf, just out of C syntax habit.

I don't understand why you'd have a note about "//calling the function", in the code, when you were just using printf() to print one char string. BFD.

if i call my original print function wont it print the numbers is reverse order since i did that before? i dont think i have the numbers set up to add correctly. im changing my add function call in main to

add(p, q);

Quote:

---

Originally Posted by Adak

It looked to me like he meant to call his own function "print", but misspelled it as printf, just out of C syntax habit.

I don't understand why you'd have a note about "//calling the function", in the code, when you were just using printf() to print one char string. BFD.

---

It could be a mistake - using prinf insttead of home made print
It could be a bad habbit - using custom string in printf instead of

Code:

---

printf("%s", string1);

---

which is more stable and thus should be recomended.

But it is not my point - my point was - compiler could not determine the first error because the prototype of the printf was match.
Maximum it could warn about the second issue - but it should be very sofisticated compiler

i cant print out the two numbers i want to add still with the add(p, q);

Quote:

---

Originally Posted by cprogrammer22

i cant print out the two numbers i want to add still with the add(p, q);

---

Is this some kind of encrypted question?

Quote:

---

Originally Posted by cprogrammer22

i cant print out the two numbers i want to add still with the add(p, q);

---

Can you post what the code is right now? Also, please explain is your problem in the printing of the strings, the printing of the answer, or getting the two strings of digits added together into one sum?

Vart: I've never seen printf() with just a pointer inside, and no formatting info. If you say it works, that's good enough for me.

Quote:

---

Originally Posted by Adak

I've never seen printf() with just a pointer inside, and no formatting info.

---

This would be the case when the format string has no format specifiers. The pointer is presumably a pointer to the first character of the format string.

Well - that's just wrong! ROFL!! :)

Quote:

---

Originally Posted by Adak

Well - that's just wrong! ROFL!! :)

---

You may dimly remember:

Code:

---

printf("Hello, world!\n");

---

Sure Tabstop - start the highly technical, complex arguments. What a pal you are!! :p :p :)

Quote:

---

Originally Posted by Adak

Sure Tabstop - start the highly technical, complex arguments. What a pal you are!! :p :p :)

---

No, it's not technical enough
Make it like this

Code:

---

const char* szSayHi = "Hello, world!\n";
printf(szSayHi);

---

Code:

---

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAXLEN 200
   
struct integer* read_integer(char* stringInt);
void print(struct integer *p);
struct integer* add(struct integer *p, struct integer *q);
struct integer* subtract(struct integer *p, struct integer *q);
int compare(struct integer *p, struct integer *q);

struct integer{
    int *digits;
    int size;
};

int main(void){
    int numlines; //Number of lines stored in the file
    char string1[MAXLEN];
    char string2[MAXLEN];
    int i;// loop index
    int opr; //Operator 1 or 2 tells us if we add or subtract
    struct integer *p;
    struct integer *q;
    struct integer *answer;

    // Open the file and read from bigint.txt
    FILE *fin;
    fin = fopen("bigint.txt","r");
    fscanf(fin, "%d", &numlines); //Read in how many lines there are in the file

    // read a line (\n)
    // read the operator(1 or 2) - forget about this one. 3 fscanf
    //scanf first sting; call read int (1st) function
    //same with the second string
    //if 1 then call add, if 2 then call subtract
    // end of loop
    for(i = 0; i < numlines; i++)
    {
        fscanf(fin, "%d", &opr);  // find out whether its add or subtract
        fscanf(fin, "%s", string1); // scan in 2nd number on the first line of input file
            p = read_integer(string1);
        fscanf(fin, "%s", string2);// scan in 3rd number on the first line of input file
            q = read_integer(string2);
   
        print(p);//call function to print out information
        printf(" ");
        print(q);
        printf("\n");

        if(opr == 1)
        {
        //add
         
          answer = add(p, q);
          print(answer = add(p, q));
        }
        else if(opr == 2)
        {
            printf("subtract here\n");
        // subtract func 
        }
    }
   

       
    fclose(fin);
    system("PAUSE");
    return 0;
}

//Preconditions: the first parameter is string that stores
//              only contains digits, doesn't start with
//              0, and is 200 or fewer characters long.
//Postconditions: The function will read the digits of the
//        large integer character by character,
//        convert them into integers and return a
//            pointer to the appropriate struct integer.
struct integer* read_integer(char* stringInt)
{
    int len;
    struct integer *myString;//create a new struct
    int i;//loop index
    //allocate memory for the struct
    myString = (struct integer*)(malloc(sizeof(struct integer)));
   
    len = strlen(stringInt); // length of the strinInt in digits
   
    myString->size = len; // length of string assigned to size in struct myString
   
    //allocate memory for digits
    myString->digits = (int*)(malloc(sizeof(int)* len));
   
    // assign number to digits, convert to integers
    for(i = 0; i < len; i++)
    {
        myString->digits[i] = stringInt [len-1-i] - '0';
    }
    return myString;
}

//Preconditions: p is a pointer to a big integer.
//Postconditions: The big integer pointed to by p is
//                printed out.
void print(struct integer *p)
{
//given pointer, want to print out digits in reverse order...
    int i;
    // no reversing in add or subtract, but want to reverse here
    for(i = p->size-1; i >= 0; i--)
    {
        printf("%d", p->digits[i]);
    }
   
}
//Preconditions: p and q are pointers to struct integers.
//Postconditions: A new struct integer is created that
//                stores the sum of the integers pointed to
//                by p and q and a pointer to it is
//                returned.
struct integer* add(struct integer *p, struct integer *q)
{
    int i;
    struct integer *addAnsw; //create new struct for answer
   
    //Allocate memory for the new struct
    addAnsw = (struct integer*)(malloc(sizeof(struct integer)));
   
    //Allocate memory for the digits in the new struct addAnsw
    addAnsw->digits = (int*)(malloc(sizeof(int)* (p->size)));
   
  for(i = 1;i <2 i++)
    {
        printf("%d + %d = %d\n", p->digits[i], q->digits[i], addAnsw->digits[i]);
        addAnsw->digits[i] = p->digits[i] + q->digits[i];
    }
   
    return addAnsw;
}

//Preconditions: p and q are pointers to struct integers.
//Postconditions: A new struct integer is created that
//                stores the absolute value of the
//                difference between the two and a pointer
//                to this is returned.
struct integer* subtract(struct integer *p, struct integer *q)
{
      struct integer *subtractAnsw;
     
      //Allocate memory for the new struct
      subtractAnsw = (struct integer*)(malloc(sizeof(struct integer)));
     
      if(p->size < q->size)
      {
            subtractAnsw->digits = (int*)(malloc(sizeof(int)*(p->size)));
      } 
}

//Preconditions: Both parameters of the function are
//          pointers to struct integer.
//Postconditions: The function compares the digits of two
//        numbers and returns:
//    -1 if the first number is smaller than the second,
//    0 if the first number is equal to the second number,
//  1 if the first number is greater than the second.

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Code:

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answer = add(p, q);
print(answer = add(p, q));

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you are calling add twice - so the first result is lost - you hav a memory loss here

of cource - while you loop - you do not free p,q and answer as well - which generates 3 more losses on each iteration

ok but that doesnt help with the add answer..

What has you confused about adding the two digits? I don't understand.

it wont print out the numbers correctly,