Test if a number is fibonacci

Question

I know how to make the list of the Fibonacci numbers, but i don\'t know how can i test if a given number belongs to the fibonacci list - one way that comes in mind is genera

Answer 1

#include 
#include 

int main()
{
int number_entered, x, y;

printf("Please enter a number.\n");
scanf("%d", &number_entered);
x = y = 5 * number_entered^2 + 4;        /*Test if 5N^2 + 4 is a square number.*/
x = sqrt(x);
x = x^2;
if (x == y)
{
        printf("That number is in the Fibonacci sequence.\n");
    }
x = y = 5 * number_entered^2 - 4;        /*Test if 5N^2 - 4 is a square number.*/
x = sqrt(x);
x = x^2;
if (x == y)
{
    printf("That number is in the Fibonacci sequence.\n");
}
else
{
    printf("That number isn't in the Fibonacci sequence.\n");
}
return 0;
}

Will this work?