Variable Resetting Issue

[Niicollas__]

I ran into some issues here, when i typed 'back' to return to the main menu of my program it reset my credits. it does this every time and i can't seem to figure out why. would anyone be able to help me with this? thanks!

#Final Project
# 1/17/2018
#This program is an arcade, with a credit system and 3 different gamemodes
#---------------------------------------------------------------------
def ws(): 
  print(" ")
import random
import time
credits = 10000         #Currency in the game 
deposit = 0 
 

def coinflip(credits,deposit):
  print("Welcome to CoinFlip!")
  print("================================")
  print("Credits:", credits)
  print("================================")
  print("Winnings Info")
  print("================================")
  print("Picking the correct side will grant you double the credits")
  ws()
  ws()
  guess = input("heads or tails? or type 'back' to go to the main menu")  #user inputs heads or tails, if they type back they will return to main menu
  if guess == "back":
    start()
  deposit = float(input("How much would you like to bet?"))               #user picks his bet ammount, and that ammount is removed from his balance
  c = ["heads", "tails"]
  coin = random.choice(c)
  credits -= deposit
  def flip():
    print("Flipping....")
    time.sleep(1.5)
    print("The coin lands on", coin)
    ws()
  
  
  if coin == "heads" and guess == "heads":
    flip()
    credits += deposit*2
    print("You Guessed Right!")
    time.sleep(1.5)
    print("You Earned", deposit*2, "Credits")
    time.sleep(1)
    print("Your Balance is now", credits, "Credits")
    time.sleep(3)
    ws()
    ws()
    ws()    
    coinflip(credits, deposit)
  elif coin == "tails" and guess == "tails":
    flip()
    credits += deposit*2
    print("You Guessed Right!")
    time.sleep(1.5)
    print("You Earned", deposit*2, "Credits")
    time.sleep(1)
    print("Your Balance is now", credits, "Credits")
    ws()
    ws()
    ws()
    coinflip(credits, deposit)
    
  else:
    flip()
    print("Sadly, you lost!")
    print("You lost", deposit, "Credits")
    print("Your balance is now", credits, "credits")
    ws()
    ws()
    ws()
    coinflip(credits, deposit)
      
 
def RPS(credits, deposit):
 ws()
 ws()
 print("Welcome to Rock, Paper, Scissors")
 print("========================================")
 print("Credits:", credits)
 print("========================================")
 print("Winnings Info")
 print("========================================")
 print("You recieve double your money for winning RPS")
 print("========================================")
 ws()
 ws()
 
 o = ["rock", "paper", "scissors"]
 comppick = random.choice(o)
           
 player = input("rock, paper, scissors? Or Type 'back' to go to the main menu")
 if player == "back":
  start()
 deposit = float(input("How much would you like to bet?"))
 player = player.lower()
 credits -= deposit
 
 def throw():
   print("Rock")
   time.sleep(0.6)
   print("Paper")
   time.sleep(0.6)
   print("Scissors")
   time.sleep(0.6)
   print("Shoot!")
   ws()



 if player == comppick:
  throw()
  credits += deposit
  print("You Chose", player)
  print("The Computer Chose", comppick)
  print("Its a tie!")
  time.sleep(3)
  RPS(credits, deposit)
  
 elif player == "rock" and comppick == "paper":
  throw()
  print("You Chose", player)
  print("The Computer Chose", comppick)
  print("You Lost!")
  time.sleep(3)
  RPS(credits, deposit)
  
 elif player == "rock" and comppick == "scissors":
  throw()
  credits += deposit * 2
  print("You Chose", player)
  print("The Computer Chose", comppick)
  print("You Win!")
  RPS(credits, deposit)
 
 elif player == "paper" and comppick == "rock":
  throw()
  credits += deposit * 2
  print("You Chose", player)
  print("The Computer Chose", comppick)
  print("You Win!")
  RPS(credits, deposit)  
 
 elif player == "paper" and comppick == "scissors":
  throw()
  print("You Chose", player)
  print("The Computer Chose", comppick)
  print("You Lost!")
  time.sleep(3)
  RPS(credits, deposit)
 
 elif player == "scissors" and comppick == "rock":
  throw()
  print("You Chose", player)
  print("The Computer Chose", comppick)
  print("You Lost!")
  time.sleep(3)
  RPS(credits, deposit)  
 
 elif player == "scissors" and comppick == "paper":
  throw()
  credits += deposit * 2
  print("You Chose", player)
  print("The Computer Chose", comppick)
  print("You Win!")
  RPS(credits, deposit)
  
  
def roulette(credits,deposit):       
  print("Roulette")
  print("===============")
  print("Credits:", credits)
  print("===============")
  print("Winnings Info")
  print("===============")
  
  print("If you land on odd or even you get 2x your credits!")
  print("If you land on your specific number you get 28x your money")
  ws()
  ws()
  num = random.randint(0,36)
  def roll():
    ws()
    print("Spinning...")
    time.sleep(1.5)
    print("It has passed", random.randint(0, 36))                           #displays to the user what the correct number is
    time.sleep(1.5)
    print("Almost lands on", random.randint(0, 36))
    time.sleep(1.6)
    print("It landed on", num)
    ws()
    ws()
  bet = input("Type 'odd', 'even' or 'specific' to pick a certain number. Or type 'back' to return to the menu.")
  if bet == "back":
    start()
  deposit = float(input("Type in how much you want to bet: "))
  credits -= deposit
      
    
  if bet == "specific":
    bet = input("Choose a number between 0 and 36")
    ws()
    
  if bet == num:                       # if bet number is = to what is rolled you win 28x your money
    credits += deposit *28
    print("Wow! You won! The number was", num)
    print("You receive", int(deposit)*28, "credits!")
    print("Your balance is now", credits, "credits")
    time.sleep(2)
    ws()
    roulette(credits,deposit)
    
        
  if num % 2 == 0 and bet == "even":    #If the number is even and you pick even you win
    roll()
    credits += deposit * 2
    print("Wow! You won! It was an even number!")
    print("You receive", int(deposit)*2, "credits!")
    print("Your balance is now", credits, "credits")
    time.sleep(2)
    ws()
    roulette(credits,deposit)      
      
  elif num % 2 != 0 and bet == "odd":
    roll()
    credits += deposit * 2                          #If the number is odd and you pick odd you win
    print("Wow! You won! It was an odd number!")
    print("You receive", int(deposit)*2, "credits!")
    print("Your balance is now", credits, "credits")
    time.sleep(2)
    ws()
    roulette(credits,deposit)      
      
  else:                                               #if the if statements above were not correct then you lost
    roll()
    print("Sadly, you lost!")
    print("You lost", deposit, "Credits")
    print("Your balance is now", credits, "credits")
    time.sleep(2)
    ws()
    roulette(credits,deposit)
 
 
 
def start():
  print("THE ARCADE")
  print("==============================")
  print("Credits:", credits)
  print("==============================")
  print("Gamemodes")
  print("==============================")
  print("coinflip")
  ws()
  print("rps")
  ws()
  print("roulette")
  print("==============================")
  ws()
  gamemode = input("Enter Desired Gamemode: ")
  if gamemode == "coinflip":
    print("You Picked CoinFlip!")
    ws()
    ws()
    ws()
    coinflip(credits, deposit)
  
  if gamemode == "rps":
    print("You Picked RPS")
    ws()
    ws()
    ws()
    RPS(credits,deposit)
  
  if gamemode == "roulette":
    print("You Picked Roulette")
    ws()
    ws()
    ws()
    roulette(credits,deposit)
start()