Question

I’m new to C and I’m having a small problem with my code:

int i, n;
int *arr;
while(n != 0) {
    scanf("%d", &n);
    if(n == 0)
        exit(1);
    else {
        arr = (int*) malloc(sizeof(int) * n);
        for(i = 0; i < n; i++)
            scanf("%d", &arr[i]);
    } //end if
} //end while

What I’m trying to do is to make an array of n size and I want to stop reading when I get a ‘0’ for example if I enter:

3
2
2
5
2
6
7
0

I want an array of size 3 with values 2, 2, 5, an array of 2 with values 6 and 7 and exit because of the 0
* Sorry, I left out an important part I think… In my code a call a calc() where I send arr, right after scanf(“%d”,&arr[i]) and then i’ll return the value and then if the next values e.g. 2 isn’t 0 I’ll read, create a new array, send arr, print result on console and again if the next value is 0 then it will exit. *
Could you guys tell me where I’m wrong?

Answer 1

The problems which are visible in your code are:
1. Checking uninitialized integer n in while. To fix this either initialize n to non zero or use a do{ ... } while() instead of while().
2. You need to validate the value of n which is read through scanf. malloc takes size_t type as the parameter which is unsigned int. But n being an integer can accept negative values, thus if a negative value is entered it will be passed as unsigned int to malloc, this may lead to undesired results (Also for loop will be executed incorrect number of times). You may also consider changing the type of n from integer to unsigned int type or change the exit condition to if( n < 1 ).
3. There is memory leak in your program. Memory allocated through malloc is not freed through free.
4. Do not assume that malloc will always succeed. Please check for the success of malloc through a NULL check i.e.

if (NULL == arr)
{
   //error handling
}

5. exit with non zero value generally indicates abnormal termination. You can use break or return. break might be a better idea as it generally gets difficult to test a function as the exit points in the function increase (though this may not be true in your case, but it is FYI)
6. Optionally, you can check the return value of scanf to make sure that a valid input was entered.

Help this helps!