Array in c ?

Question

Why can't able to get value and print the value in the same Loop

int main(void){
int num;
scanf("%d", &num);

int fibonacci[num];
for (i = 2; i < num; i++){
finbonacci[i] = fibonacci[i - 2] + fibonacci[i - 2];
printf("%d", fibonacci[i]);
}
}

It returns an unpredictable output

Answer 1

There are many mistakes in your code
1. In the for loop declaration `for(i = 2; .....)`, you have not given the type of `i`
2. In the line, `finbonacci[i] = fibonacci[i - 2] + fibonacci[i - 2]`, note that you have written `finbonacci` instead of `fibonacci`

After fixing these, your code will compile, but will give an undefined behaviour
Try to visualize what happens in the loop
1st iteration:
fibonacci[i] = fibonacci[i - 2] + fibonacci[i - 2]
i = 2
fibonacci[2] = fibonacci[0] + fibonacci[0]
Here your code is accessing fibonacci[0], which is uninitialized because you have not assigned a value to it. You will need to give the values for the 0th and 1th index of the fibonacci array, like so
fibonacci[0] = 0;
fibonacci[1] = 1;

You code will now compile and give numbers that make sense, but will still not give the correct output. In the same line,
fibonacci[i] = fibonacci[i - 2] + fibonacci[i - 2]
you are adding `fibonacci[i - 2]`. Maybe you wanted one of them to be `fibonacci[i - 1]`?

Answer 2

/* Program to generate fibonacci number */
#include <stdio.h>
int main(void)
{
int num, i;

printf("Enter a number :");
scanf("%d", &num);

int fib[num];

// Begins
for (i = 0; i <= num; i++){
fib[i] = fib[i - 2] + fib[i - 1];
printf("%d\n", fib[i]);
}
}
hey it's my code I just write the above with my mobile

My mistake is I forgot to initialize 0 and 1 as 0 and 1
thank you so much