Passing argument 2 of 'fibonacci' from incompatible pointer type

Question

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

//Fibonacci

void fibonacci(int n, int *fibs[n]){

    int i;
    *fibs[0] = 1;
    *fibs[1] = 1;

    printf("%d %d ", *fibs[0], *fibs[1]);

    for(i=2; i<=n; i++){
        *fibs[i] = *fibs[i-1] + *fibs[i-2];
        printf("%d ", *fibs[i]);
    }   
}

int main(){

    int n, i;

    printf("How many fibonacci numbers do you want to enter?: ");
    scanf("%d", &n);
    int fibs[n];

    fibonacci(n, &fibs);
    
    return 0;
}

I was writing a Fibonacci program in this way. The program runs but does not print anything. And I get the error like, [Warning] passing argument 2 of 'fibonacci' from incompatible pointer type How can I fix this program to run efficiently?

Answer 1

You declared a variable length array

int fibs[n];

In this call

fibonacci(n, &fibs);

the argument has the type int ( * )[n].

However the corresponding function parameter

void fibonacci(int n, int *fibs[n]){

has the type int ** (due to adjusting by the compiler the parameter having array type to pointer to the array element type).

So the compiler issues the message.

The function declaration can be much simpler

void fibonacci(int n, int fibs[n]){

And in this case the function is called like

fibonacci(n, fibs);

Of course you will need to change the body of the function.

Pay attention to that this loop

for(i=2; i<=n; i++){

can result in accessing memory outside the passed array when i is equal to n because the valid range of indices is [0, n).

And the first two Fibonacci numbers are 0 and 1.

Even in the very beginning of the function

int i;
*fibs[0] = 1;
*fibs[1] = 1;

you need to check whether n is not less than 2.

The function can look for example like

void fibonacci( int a[], size_t n )
{
    if ( !( n < 1 ) ) a[0] = 0;
    if ( !( n < 2 ) ) a[1] = 1;

    for ( size_t i = 2; i < n; i++ )
    {
        a[i] = a[i-1] + a[i-2];
    }
}

and called like

size_t n = 0;

printf("How many fibonacci numbers do you want to enter?: ");
scanf( "%zu", &n );

if ( n != 0 )
{
    int fibs[n];

    fibonacci( fibs, n );
}