Fibonacci sequence does not work [closed]

The second conditional block was incorrect, because if the variable i was different from 1 or 2 it would enter else , so Fib [0] was wrong.

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

int main(){

    int i, Fib[100], n;

    scanf("%d",&n);

    for(i = 0; i < n; i++){
        if(i == 0){
            Fib[i] = 0;
        } 
        else if(i == 1 || i == 2){
            Fib[i] = 1;
        }
        else{
            Fib[i] = Fib[i-1] + Fib[i-2];
        }
        printf("Fib[%d] = %d \n", i, Fib[i]);
    }

    return 0;
}

The reason for being wrong is that the logic is too complex. If you follow the definition of Fibonacci it becomes simpler.

The definition says that the sequence starts with 0 and 1, so start the sequence with 0 and 1 explicitly. After that you do not have to deal with anything, you do not have to condition what you're going to do. It gets simpler and faster.

The definition does not speak in a sequence that has exceptions in certain elements. Set the problem correctly and the solution comes out more fluid.

I kept the array because it might be a requirement, but it's completely unnecessary to just print a Fibonacci sequence.

#include <stdio.h>

int main() {
    int fib[100];
    int n;
    scanf("%d", &n);
    fib[0] = 0;
    fib[1] = 1;
    n--;
    for (int i = 2; i < n; i++) fib[i] = fib[i - 1] + fib[i - 2];
    for (int i = 0; i < n; i++) printf("%d ", fib[i]);
}

See running on ideone . And in Coding Ground . Also put it in GitHub for future reference .

You can work with type unsigned long long that has 64bits size, making it possible to generate fibonacci sequences up to 91 numbers:

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

#define MAX_FIBO_SEQ   (91)

typedef unsigned long long uint64_t;  /* ( (2^64) - 1 ) = 18.446.744.073.709.551.615 max. */

int fibonacci( uint64_t f[], int n )
{
    int i = 0;

    if( n <= 0 )
        return -1;

    if( n > MAX_FIBO_SEQ )
        n = MAX_FIBO_SEQ;  /* Nao permite overflow */

    f[0] = 1;

    if( n == 1 )
        return n;

    f[1] = 1;

    if( n == 2 )
        return n;

    for( i = 2; i < n; i++ )
        f[i] = f[i - 2] + f[i - 1];

    return n;
}


int main( int argc, char * argv[] )
{
    int i = 0;
    int n = atoi(argv[1]);
    uint64_t seq[ MAX_FIBO_SEQ ];

    /* Preenche array 'seq' com uma sequencia dos 'n' primeiros
       numeros da serie de Fibonacci... */
    n = fibonacci( seq, n );

    /* Exibe array */
    for( i = 0; i < n; i++ )
        printf("%s%lld", (i)?", ":"", seq[i] );
    printf("\n");

    return 0;
}

Test # 1:

$ ./fibo 10
1, 1, 2, 3, 5, 8, 13, 21, 34, 55

Test # 2:

$ ./fibo 91
1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584, 4181, 6765, 10946, 17711, 28657, 46368, 75025, 121393, 196418, 317811, 514229, 832040, 1346269, 2178309, 3524578, 5702887, 9227465, 14930352, 24157817, 39088169, 63245986, 102334155, 165580141, 267914296, 433494437, 701408733, 1134903170, 1836311903, 2971215073, 4807526976, 7778742049, 12586269025, 20365011074, 32951280099, 53316291173, 86267571272, 139583862445, 225851433717, 365435296162, 591286729879, 956722026041, 1548008755920, 2504730781961, 4052739537881, 6557470319842, 10610209857723, 17167680177565, 27777890035288, 44945570212853, 72723460248141, 117669030460994, 190392490709135, 308061521170129, 498454011879264, 806515533049393, 1304969544928657, 2111485077978050, 3416454622906707, 5527939700884757, 8944394323791464, 14472334024676221, 23416728348467685, 37889062373143906, 61305790721611591, 99194853094755497, 160500643816367088, 259695496911122585, 420196140727489673, 679891637638612258, 1100087778366101931, 1779979416004714189, 2880067194370816120, 4660046610375530309