g++ compiler is not recognizing my function

Question

I'm just starting to code, and am learning about arrays right now. I am trying to write a program that takes in a list of arrays, and tells me if the first or last number is a 2. To do this, I'm using a function.

My code looks like:

    #include <iostream>
    using namespace std;

    const int size = 6;
    bool firstlast(int array[size]);

    int main()
    {
        int array[size];
        for (int index = 0; index < size; index++)
        {
            cout << "Enter value for array[" << index << "]\n";
            cin >> array[index];
        }

        bool check = firstlast(array[size]);
        if (check)
            cout << "The array either starts or ends in 2!\n";
        else 
            cout << "The array does not start or end with 2.\n"; 
        return 0;
    }

    bool firstlast(int array[size])
    {
        if (array[0] == 2)
            return true;
        if (array[size - 1] == 2)
            return true;
        return false;
    }

What am I doing wrong? The compiler gives me the error:

candidate function not viable: no known conversion from 'int' to 'int *' for 1st argument; take the address of the argument with and

The declaration should be `bool firstlast(int array[size]);` - it needs to be consistent with the function definition and provide the type of the array. — John D, Oct 01 '16 at 02:11
Your function, when corrected, takes an array, not a 'list of arrays'. You probably need to show how you're calling it — what the arguments look like and how they are declared. — Jonathan Leffler, Oct 01 '16 at 02:13
You can't take an array parameter like that. Jonathan's wrong: you don't take an array; you take a pointer. Yes, despite the characters you wrote. — Lightness Races in Orbit, Oct 01 '16 at 02:14
I made a typo in my code. I did declare the function as bool firstlast(int array[size]); but it doesn't work — Josh Simani, Oct 01 '16 at 02:16
Which book are you using to learn C++? It's teaching you wrong. — Lightness Races in Orbit, Oct 01 '16 at 02:16
@JoshSimani Show a [MCVE] including the function call please. — πάντα ῥεῖ, Oct 01 '16 at 02:27

score 1 · Answer 1 · answered Oct 01 '16 at 02:53

The compiler is recognising your function fine.

The problem is in the manner your code calls the function

bool check = firstlast(array[size]);

which attempts to pass array[size] (a non-existent element of array) to a function expecting a pointer.

The call, presumably, should be

bool check = firstlast(array);

since arrays are implicitly converted to pointers when passed to functions.

score 0 · Answer 2 · answered Oct 01 '16 at 02:51

0

This code

bool check = firstlast(array[size], size);

tries to pass the sizeth element of array not the array itself. In C++ arrays are passed by pointer, even if you write the function parameter with array syntax.

To avoid confusing yourself, change firstlast to

bool firstlast`(int* array, int size)`

and call it with

bool check = firstlast(array, size);

answered Oct 01 '16 at 02:51

kfsone

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Thanks! But why do I need to include the "int size" in the parameter? – Josh Simani Oct 01 '16 at 03:01
@JoshSimani Because that info would get lost otherwise. Also see [here](http://stackoverflow.com/questions/1461432/what-is-array-decaying) please. – πάντα ῥεῖ Oct 01 '16 at 03:20

g++ compiler is not recognizing my function

2 Answers2