fibonacci.c

#include <stdio.h>

int fibonacci(int num);

int main() {
  int i;
  printf("Enter number:\n");
  int result = scanf("%d", &i);

  if (result == 0) {
    printf("Need integer input!\n");
    return 1;
  } else if (i < 0) {
    printf("Need natural number!\n");
    return 1;
  }

  printf("Fibonacci number: %d\n", fibonacci(i));

  return 0;
}

int fibonacci(int num) {
  if (num == 0) {
    return num;
  } else if (num == 1) {
    return num;
  } else {
    num = fibonacci(num - 1) + fibonacci(num - 2);
    return num;
  }
}