💻 Fibonacci Series

def fibonacci_list(n):
    if n <= 0: return []
    if n == 1: return [0]
    fib = [0, 1]
    for i in range(2, n):
        fib.append(fib[-1] + fib[-2])
    return fib

def fibonacci_recursive(n):
    if n <= 1: return n
    return fibonacci_recursive(n-1) + fibonacci_recursive(n-2)

def is_fibonacci(num):
    fib = fibonacci_list(100)
    return num in fib

print("=== Fibonacci Series ===")
while True:
    print("
1. N terms ki Fibonacci series")
    print("2. Nth Fibonacci number")
    print("3. Check: kya yeh Fibonacci number hai?")
    print("4. Golden Ratio dekho")
    print("5. Baahar jao")
    ch = input("Choice: ")
    if ch == "1":
        n   = int(input("Kitne terms: "))
        fib = fibonacci_list(n)
        print(f"Fibonacci ({n} terms):")
        print(f"  {fib}")
        print(f"  Sum: {sum(fib)}")
    elif ch == "2":
        n = int(input("N (1-20): "))
        print(f"{n}th Fibonacci: {fibonacci_list(n+1)[-1]}")
    elif ch == "3":
        num = int(input("Number check karo: "))
        if is_fibonacci(num):
            print(f"{num} EK Fibonacci number hai!")
        else:
            print(f"{num} Fibonacci number NAHI hai!")
    elif ch == "4":
        fib = fibonacci_list(15)
        print("
Golden Ratio (consecutive terms ka ratio):")
        for i in range(2, min(10, len(fib))):
            if fib[i-1] != 0:
                ratio = fib[i] / fib[i-1]
                print(f"  {fib[i]:4} / {fib[i-1]:3} = {ratio:.6f}")
    elif ch == "5":
        break