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Why does the amount is incorrect?

+3 votes
asked Nov 20 by Lexus Guevara (560 points)
#include <stdio.h>

int
main ()
{
  char meal;
  char drinks;
  char A, B, C, D, S, M, L;
  int quantity;
  int amount;
  char order;

  printf ("\tMeal\t\tPackage\t\t\t\tPrice\n");
  printf ("\tA   \t\tChicken & Spaghetti\t\t150\n");
  printf ("\tB   \t\tHamburger & Fries  \t\t145\n");
  printf ("\tC   \t\tCheese Burger      \t\t100\n");
  printf ("\tD   \t\tPizza              \t\t80\n\n");
  printf ("\tDrinks   \tDescription\t\t\tPrice\n");
  printf ("\tS   \t\tSmall Drinks \t\t\t30\n");
  printf ("\tM   \t\tMedium Drinks\t\t\t35\n");
  printf ("\tL   \t\tLarge Drinks \t\t\t40\n\n");
    
    
    
  printf("Enter your meal (A, B, C, D, E) : ");
  scanf("%c", &meal);
  printf("Enter your drink (S, M, L) : ");
  scanf(" %c", &drinks);
  printf("Quantity : ");
  scanf(" %d", &quantity);
    
  printf("\nMeal          : %c", meal);
  printf("\nDrinks        : %c", drinks);
  printf("\nQuantity      : %d", quantity);
  
  switch(meal){
      case 'A':
        A = 150;
        switch(drinks){
            case 'S':
                S = 30;
                amount = (A + S) * quantity;
                printf("\nOrder Details : Chicken & Spaghetti and Small Drinks");
                break;
            case 'M':
                M = 35;
                amount = (A + M) * quantity;
                printf("\nOrder Details : Chicken & Spaghetti and Medium Drinks");
                break;
            case 'L':
                L = 40;
                amount = (A + L) * quantity;
                printf("\nOrder Details : Chicken & Spaghetti and Large Drinks");
                break;
        }
        break;
        
      case 'B':
        B = 145;
        switch(drinks){
            case 'S':
                S = 30;
                amount = (B + S) * quantity;
                printf("\nOrder Details : Hamburger & Fries and Small Drinks");
                break;
            case 'M':
                M = 35;
                amount = (B + M) * quantity;
                printf("\nOrder Details : Hamburger & Fries and Medium Drinks");
                break;
            case 'L':
                L = 40;
                amount = (B + L) * quantity;
                printf("\nOrder Details : Hamburger & Fries and Large Drinks");
                break;
        }
        break;
        
      case 'C':
        C = 100;
        switch(drinks){
            case 'S':
                S = 30;
                amount = (C + S) * quantity;
                printf("\nOrder Details : Cheese Burger and Small Drinks");
                break;
            case 'M':
                M = 35;
                amount = (C + M) * quantity;
                printf("\nOrder Details : Cheese Burger and Medium Drinks");
                break;
            case 'L':
                L = 40;
                amount = (C + L) * quantity;
                printf("\nOrder Details : Cheese Burger and Large Drinks");
                break;
        }
        break;
        
      case 'D':
      D = 80;
      switch(drinks){
            case 'S':
                S = 30;
                amount = (D + S) * quantity;
                printf("\nOrder Details : Pizza & Fries and Small Drinks");
                break;
            case 'M':
                M = 35;
                amount = (D + M) * quantity;
                printf("\nOrder Details : Pizza & Fries and Medium Drinks");
                break;
            case 'L':
                L = 40;
                amount = (D + L) * quantity;
                printf("\nOrder Details : Pizza & Fries and Large Drinks");
                break;
      }
      break;
      
    default:
        printf("Invalid Order Details");
  }

  printf("\nAmount        : %d", amount);
  
  

  return 0;
}

1 Answer

0 votes
answered Nov 20 by Peter Minarik (40,320 points)

Solution For Your Problem

The problem is that your variables A, B, C, D, S, M, L are of type char. A char is an integral type taking value in a range of [-128, 127]. These variables are supposed to represent the price of a certain food.

When you assign A = 150, then the actual value stored in A is -106 as it overflows (128 - 150 = 22 overflow, hence -128 - 22 = -106). Similarly, when you add to chars together the chances are that you cannot store the result on just one signed byte (char). Instead, use a larger type, e.g. int.

And Some Extra...

You could restructure your code in a way that data and logic is separated. You could create functions that deal with processing various food requests or displaying them. You could create a data structure that holds the code, the name and the price of a specific food item.

If you do this, your program is easily extendable. If you want to add a new meal or drink, you just add it to the right array and voila, everything works. No need to touch anything else, no extra switch-cases, no extra logic needed.

See an example for this below:

#include <ctype.h>
#include <stdio.h>

#define CODE_LENGTH 8
#define NAME_LENGTH 24
#define PRICE_LEN 8

#define ElementCount(array) sizeof(array) / sizeof(array[0])

typedef struct
{
    char code;
    const char * name;
    int price;
} Food;

// columns must have exactly 3 elements
void PrintHeader(const char ** columns)
{
    printf("%-*s%-*s%*s\n", CODE_LENGTH, columns[0], NAME_LENGTH, columns[1], PRICE_LEN, columns[2]);
}

void PrintFood(const Food * foods, size_t numFoods)
{
    for (size_t i = 0; i < numFoods; i++)
        printf("%-*c%-*s%*d\n", CODE_LENGTH, foods[i].code, NAME_LENGTH, foods[i].name, PRICE_LEN, foods[i].price);
}

const Food * Find(const Food * foods, size_t numFoods, char code)
{
    for (size_t i = 0; i < numFoods; i++)
    {
        const Food * food = &foods[i];
        if (food->code == code)
            return food;
    }
    return NULL;
}

int main()
{
    //
    // Setting up the menu
    //
    const char * mealHeader[] = { "Meal", "Package", "Price" };
    Food meals[] =
    {
        { 'A', "Chicken & Spaghetti", 150 },
        { 'B', "Hamburger & Fries", 145 },
        { 'C', "Cheese Burger", 100 },
        { 'D', "Pizza", 80 }
    };

    const char * drinkHeader[] = { "Drinks", "Description", "Price" };
    Food drinks[] =
    {
        { 'S', "Small Drinks", 30 },
        { 'M', "Medium Drinks", 35 },
        { 'L', "Large Drinks", 40 }
    };
    
    //
    // Printing the menu
    //
    PrintHeader(mealHeader);
    PrintFood(meals, ElementCount(meals));
    printf("\n");
    PrintHeader(mealHeader);
    PrintFood(drinks, ElementCount(drinks));
    printf("\n");
    
    //
    // Asking the user to choose something from the menu
    //
    char meal;
    char drink;
    int quantity;
    printf("Enter your meal (A, B, C, D, E) : ");
    scanf("%c", &meal);
    printf("Enter your drink (S, M, L) : ");
    scanf(" %c", &drink);
    printf("Quantity : ");
    scanf(" %d", &quantity);
    printf("\n");
    printf("--------------------------------------------")
    printf("\n");
    
    //
    // Processing the user's choice
    //
    const Food * orderedMeal = Find(meals, ElementCount(meals), toupper(meal));
    if (!orderedMeal)
    {
        printf("Invalid meal code: %c\n", meal);
        return -1;
    }

    const Food * orderedDrink = Find(drinks, ElementCount(drinks), toupper(drink));
    if (!orderedDrink)
    {
        printf("Invalid drink code: %c\n", drink);
        return -1;
    }
    
    int total = (orderedMeal->price + orderedDrink->price) * quantity;
    printf("Meal         : %c\n", meal);
    printf("Drink        : %c\n", drink);
    printf("Quantity     : %d\n", quantity);
    printf("Order details: %s and %s\n", orderedMeal->name, orderedDrink->name);
    printf("Amount       : %d", total);
    return 0;
}
commented Nov 21 by Lexus Guevara (560 points)
thank you very much, I'm sorry I don't understand the syntax you had used yet, but I will try to learn this. Thank you!
commented Nov 21 by Lexus Guevara (560 points)
also, i tried to look into your first suggestion, so I added an int a, b, c, d, s, m, l; and replace the uppercase char types in my switch cases. But thanks to you that you gave me a better solution and suggestion
commented Nov 21 by Peter Minarik (40,320 points)
"I don't understand the syntax you had used"

Please, look at how formatting works for printf(): https://www.cplusplus.com/reference/cstdio/printf/

If this is not what you meant, I'm happy to clarify if you have any specific questions.
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