Benötige euere Hilfe bei meinem C Programm (Funktionen)

#include <stdio.h>

int counter;

    int selection;

  int quantity;

    double money;

  double total_cost=0;

  double price;

  double sum;

  double change;

    int menu();

  int FoodSelected (int selection);

  double ItemCost(int selection);

  double totalprice(double price, int quantity);

    double EnteredMoney(double money, double sum);

int main()

{

  int counter;

    int selection;

  int quantity;

    double money;

  double total_cost=0;

  double price;

  double sum;

  double change;

    // write the code to print the first 4 lines of the output image in the output file //

  FILE *fp;

    fp  = fopen ("invoice.txt", "w");

    fprintf(fp, "The bill info of the selected item is:\n");

    fprintf(fp, "--------------------------------------------------------------------------------:\n");

    fprintf(fp, "The bill info of the selected item is:\n");

    fprintf(fp, "Item \t Price \t Quantity \t Total \t Paid Money \t Remaining Money\n");

    fprintf(fp, "--------------------------------------------------------------------------------:\n");

  for (counter=1, counter > 0, ++counter)

  {

    int menu ();

    if (selecion != 5)

    {

      int FoodSelected (int selection);

      double ItemCost(int selection);

      double totalprice(double price,int quantity);

      if (selection ==1)

      {

        fprintf(fp, "Apple\t  %f \t %d  \t %f \n", &price, &quantity, &total_cost);

      }

      else if (selection ==2)

      {

        fprintf(fp, "Banana\t  %f \t %d  \t %f \n", &price, &quantity, &total_cost);

      }

      else if (selection ==3)

      {

        fprintf(fp, "Orange\t  %f \t %d  \t %f \n", &price, &quantity, &total_cost);

      }

      else (selection ==4)

      {

        fprintf(fp, "Salad\t  %f \t %d  \t %f \n", &price, &quantity, &total_cost);

      }

      sum = sum + total_cost;

      printf("------------------------------------------");

    }

    else (selecion == 5)

    {

      printf("Please enter the Money");

      printf("\n");

        scanf("%f",&money);

      printf("\n");

      double EnteredMoney(double money, double sum);

      fprintf(fp, "--------------------------------------------------------------------------------:\n");

      fprintf(fp, "\t\t\t\t %d $\t %f $ \n", &money, &change);

      break;

    }

  }

  printf("Thank you for your payment, please check the reset file which has your payment details\n");

  fclose (fp);

  return 0;

  menu();

  int FoodSelected(int selection);

  int ItemCost(int selection);

  double totalprice(double price, int quantity);

    double EnteredMoney(double money, double sum);

  return 0;

}

/* Menu Function */

int menu ()

  {

    /*List the menu on the screen*/

    printf("MENU: ");

    printf("\n");

    printf("1. Apple                   $1.00\n");

    printf("2. Banana                  $1.50\n");

    printf("3. Orange                  $2.00\n");

    printf("4. Salad                   $3.00\n");

    printf("5. Quit");

    printf("\n\n");

    /* Ask the user to choose an option from the menu*/

    printf("Please enter your selection: ");

    scanf("%d",&selection);

    printf("\n");

    return selection;

  }

/* Food Selection Function */

/* This function displays the selected item by the user and ask him how many of that item he needs*/

int FoodSelected (int selection)

  {

  if (selection==1)

    {

      printf("You have selected Apple.                   $1.00 ");

      printf("\n");

      printf("How many of the item you need\n");

        scanf("%d",&quantity);

    }

  else if (selection==2)

    {

      printf("You have selected Banana.                   $1.50 ");

      printf("\n");

      printf("How many of the item you need\n");

        scanf("%d",&quantity);

    }

  else if (selection==3)

    {

      printf("You have selected Orange.                   $2.00 ");

      printf("\n");

      printf("How many of the item you need\n");

        scanf("%d",&quantity);

    }

  else if (selection==4)

    {

      printf("You have selected Salad.                   $3.00 ");

      printf("\n");

      printf("How many of the item you need\n");

        scanf("%d",&quantity);

    }

  else                                  /* If the user enter a value that is not between 1-5*/

    {

      printf("Invalid selection! Please try again.");

      scanf("%d",&selection);

      printf("\n");

      int FoodSelected (int selection);

    }

  return quantity;

  }

/* Selected Item Cost Function */

/* This funtion defines the value of the item selected by the user*/

double ItemCost(int selection)

  {

  if (selection==1)

    {

      price = 1.00;

    }

  else if (selection==2)

    {

      price = 1.50;

    }

  else if (selection==3)

    {

      price = 2.00;

    }

  else if (selection==4)

    {

      price = 3.00;

    }

  return price;

  }

/* Total Item Cost Function */

/* This finction calculates the total cost of the item. It is the price multiplies by the quantity*/

double totalprice(double price,int quantity)

  {

    total_cost = price*quantity;

    return total_cost;

  }

/* Entered Money and return change Functions */

/* This function calculates the change and checks if the money value is valid*/

double EnteredMoney(double money, double sum)

    {

            double change;

      if (money >= sum)

      {

        change = money - sum;

      }

      else

      {

      printf("Error! Please enter the money again!!\n");

      scanf("%f",&money);

      printf("\n");

      double EnteredMoney(double money, double sum);

      }

      return change;

    }

/* Main Function */