Finding the closest fibonacci numbers

Question

I am trying to solve a bigger problem, and I think that an important part of the program is spent on inefficient computations.

I need to compute for a given number N, th

Answer 1

A number is Fibonacci if and only if one or both of (5*n^2 + 4) or (5*n^2 – 4) is a perfect square. I am using this premise to verify if the input number belongs to a fibonacci series or not.

#include 
#include 
#include 
#include 
#include 

typedef struct node{

    int64_t value;
    struct node *next;

}Node;

Node *head ;

void readElements(int);
int isPerfectSquare(int64_t sqrValue);

int main(){

    int input_count , flag=0;
    Node *temp_node = NULL;
    int64_t sqrValue = 0;

    scanf("%d" , &input_count);

    if((input_count < 1 )||(input_count > 100000)){
        printf("Total number of Inputs out of Range ..!!\n");
        return 1;
    }

    readElements(input_count);

    /*Reading the elements from the list*/

    temp_node = head;

    while(temp_node != NULL){

        sqrValue = 5*pow(temp_node->value , 2);
        flag = (isPerfectSquare(sqrValue+4) || isPerfectSquare(sqrValue-4));

        if(flag == 1){
            printf("IsFibo\n");
        }
        else{
            printf("IsNotFibo\n");
        }

        temp_node = temp_node->next;

    }   



    return 0;

}


void readElements(int input_count){

    int temp = 0;
    int64_t val = 0;
    Node *temp_node =NULL , *cur = NULL;
    char b[20];


    while (temp < input_count) {

        scanf("%s" , b);
        val = atol(b);

        if(val < 0 || val >10000000000)
            continue;

        temp_node = (Node*) malloc(sizeof(Node));

        temp_node->value = val;
        temp_node->next = NULL;

        if(head == NULL){
            head = cur = temp_node;
        }
        else{
            cur->next = temp_node;
            cur = temp_node;
        }

        temp++;

    }

}

int isPerfectSquare(int64_t sqrValue){

    int64_t s = 0;

    s = sqrt(sqrValue);

    return(s*s == sqrValue);

}