割引コード..どこが間違っていましたか？

Question

このコードは、顧客の数量に基づいて商品の最終価格を提示するように設計されています。私はすでに方程式を追加しましたが、それが実行されたときに割引と最終価格は正しく評価されていません。擬似コードのどこが間違っているかを誰かが知っていれば、とても役に立ちます。

using namespace std; 
int main() { 

    // Variables 
    double Retail, quantity, discount1, discount2, discount3, discount4, TotalCost1, TotalCost2, TotalCost3, TotalCost4; 
    Retail = 99; 
    quantity = 0; 
    discount1 = (quantity * Retail) * .20; 
    discount2 = (quantity * Retail) * .30; 
    discount3 = (quantity * Retail) * .40; 
    discount4 = (quantity * Retail) * .50; 
    TotalCost1 = quantity - discount1; 
    TotalCost2 = quantity - discount2; 
    TotalCost3 = quantity - discount3; 
    TotalCost4 = quantity - discount4; 

    //Equations 
    cout << "Please enter the quantity of items you would like to purchase: " << endl; 
    cin >> quantity; 
    cout << "The number of items being purchased is: " << quantity << endl; 

    if (quantity <= 19) { 
     cout << "Your final price is: " << discount1 << endl; 
    } 
    if (quantity >= 20) { 
     cout << "Your final price is: " << discount2 << endl; 
    } 
    if (quantity >= 50) { 
     cout << "Your final price is: " << discount3 << endl; 
    } 
    if (quantity >= 100) { 
     cout << "Your final price is: " << discount4 << endl; 
    } 




     system("pause"); 
} 

Answer 1

割引を計算する前に、数量が0以外のものとして定義されていないということだけですか？私は計算の前にあなたの購入の読書を移動し、（オンラインコンパイラを使用して）良い結果を得た。

double Retail, quantity, discount1, discount2, discount3, discount4, TotalCost1, TotalCost2, TotalCost3, TotalCost4; 
Retail = 99; 
quantity = 0; 

//Equations 
cout << "Please enter the quantity of items you would like to purchase: " << endl; 
cin >> quantity; 
cout << "The number of items being purchased is: " << quantity << endl; 

discount1 = (quantity * Retail) * .20; 
discount2 = (quantity * Retail) * .30; 
discount3 = (quantity * Retail) * .40; 
discount4 = (quantity * Retail) * .50; 
TotalCost1 = quantity - discount1; 
TotalCost2 = quantity - discount2; 
TotalCost3 = quantity - discount3; 
TotalCost4 = quantity - discount4; 


if (quantity <= 19) { 
    cout << "Your final price is: " << discount1 << endl; 
} 
if (quantity >= 20) { 
    cout << "Your final price is: " << discount2 << endl; 
} 
if (quantity >= 50) { 
    cout << "Your final price is: " << discount3 << endl; 
} 
if (quantity >= 100) { 
    cout << "Your final price is: " << discount4 << endl; 
} 


Please enter the quantity of items you would like to purchase: 
The number of items being purchased is: 19 
Your final price is: 376.2