Odtnhj

I've been asked to write a code that takes 2, 1D arrays from a text file, add them and then return the results to another text file. Yet, I still get errors about pointers. I'm a C newbie and I'll be very happy if someone could explain it to me.

Here's the code, the result array is global.All the variable names are in Polish, I hope that's not a problem.

int dzialanie(int a, int b)

 int *wsk = &c_tab[0];
 char wybor;
 printf("0.Suman1.Roznica");
 scanf("%c", &wybor);
 for (i=0; i<9; i++) 
 if (wybor == '0')
 
 *wsk = a[i] + b[i];
 wsk++;
 
 else if (wybor == '1')
 
 *wsk = a[i] - b [i];
 wsk++
 
 
 return *wsk;

The first error I see is that you need to declare the function type with the type of the returned value, in this case the function has to be:

int *dzialanie(int a, int b)
 ...
 return wsk;

Another error is in the for loop, the operation has to be:

...
for (int i=0; i<9; i++)
 *(wsk + i) = a[i] + b[i];

...

Same for the another (See that you didn't declare the i which is a variable too). Another way, is doing:

wsk[i] = a[i] - b[i];

Is the same.
If you already know the dimension of the two arrays, maybe is better to take the arguments as pointers, it will look like:

int dzialanie(int *a, int *b)
 ...
 

And you will have to allocate memory, this coul be done with malloc:

wsk = (int *)malloc(10*sizeof(int));

At the end of your program you will want to free that allocated memory, doing:

free(wsk);

Hope you understand, my english is poor, I'm from Argentina. Greetings!

since you are using a global variable the return type should be void(and or some form of indication that the calculation has been done. which in turn could be a simple return value of -1 or w/e(i'll leave that part up to you).

int res[10]; // global variable

void add(int *a, int *b) // no return value, new array will be saved globally(not advisable)

 int sign = -1; // your +- check
 printf("0.Suman1.Roznica");
 scanf("%c", &sign);
 if (sign == 0)
 
 for (int i = 0; i < 9; i++)
 res[i] = a[i] + b[i]; 
 
 else if (sign == 1)
 
 for (int i = 0; i < 9; i++)
 res[i] = a[i] - b[i]; 
 

an alternative way of doing it would be to use either a or b as "return" values with a simple change like a[i] += b[i] -> now a has the value of a + b. this way you won't have to deal with pointers going out of scope etc(documentation of how to return pointers from functions(in a safe way) is here).