Printing list backwards - c++

Question

I am having a problem with this program which is to print out a list forwards and backwards, however When I print out the list backwards the first number in the list is a random massive number rather than the right number. e.g.
0 1 2 3 4 5 6 7 8 0
4286398 8 7 6 5 4 3 2 1 0
can anyone explain what is wrong with my code please.
Also Can anyone tell me how I could pass the counter from the printList function to a new function called checkList() so that the counter has the same value in checkList() as what it is at the end of printList().
code:
void printList(int array1[]){
int counter = 0;
int x;
ifstream theFile("list.txt");
while(theFile >> x){
array1[x] = x;
cout << array1[x] << " ";
counter = counter + 1;
}
cout << endl << counter << endl;;
int n = counter;
for(int i = n -1; i >= 0; i--){
cout << array1[i] << " ";
}

Answer 1

Here's the culprit:
array1[x] = x;
If your array input values are 0 1 2 3 4 5 6 7 8 0, then at the last iteration of your loop you're doing array1[0] = 0. That overwrites the first item in your array, while incrementing the counter. Then, when you reverse it array[9] contains garbage value because you never set it.

Answer 2

You have a problem because of the line array1[x]=x;. Your code would actually work if the numbers in your file were 0..9, but the final number is another 0, so you don't set array1[9] to anything.
You should have some variable for indexing the array, something like:
int counter = 0;
while(theFile >> x){
array1[counter] = x;
cout << array1[counter] << " ";
counter = counter + 1;
}

Answer 3

you are doing
array1[0] = 0;
array1[1] = 1;
array1[2] = 2;
array1[3] = 3;
array1[4] = 4;
array1[5] = 5;
array1[6] = 6;
array1[7] = 7;
array1[8] = 8;
array1[0] = 0; // here
array1[9] is uninitialized

Answer 4

You have some serious issues in the code:
ifstream theFile("list.txt");
while(theFile >> x){
array1[x] = x;//^^this is evil
cout << array1[x] << " ";
counter = counter + 1;
}
cout << endl << counter << endl;;
//^^extra colon, though not wrong here but not good practice
You read from file and fill the array, in your special case, you have:
0 1 2 3 4 5 6 7 8 0
You have 10 elements, but your array1 will end up with 9 since the last read was 0 and array1[0] was written as 0 again. So when you output your array1, you will never get 10 numbers since your array actually stores 9 numbers. that's why you saw garbage value if you try to access array1[9], which value has not been filled, some garbage raw memory value.
Instead, you can try to do the following:
int counter = 0;
int x;
ifstream theFile("list.txt");
while(theFile >> x){
array1[counter] = x;
cout << array1[counter] << " ";
counter = counter + 1;
}
cout << endl << counter << endl;;

Answer 5

You are counting wrong upwards and eventually hit uninitialized memory AFTER your array. You should pass the length of your array as a parameter to your function.
As arrays decay to pointers you won't be able to recover its length.
void printList(int array1[], into size){ }
Then thou don't need to figure out its length so complicated.