Cell phone company bill calculation in C++.

CellPhoneCompany.cpp

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+#include<bits/stdc++.h>
+#include<iomanip>
+using namespace std;
+//This function will return bill amount for a regular customer;
+double regularBill(double minutes)
+{
+    double cost;
+    //if total spent time is less than equal 50 minutes then it's free of cost, only regular bill cost have to pay
+    if(minutes <= 50)
+        minutes = 0;
+    else    //else first 50 minutes is free and after 50 minutes for each minute 0.2 will be charged;
+        minutes -= 50;
+    cost = 10 + minutes * 0.20;
+    return cost;    //return regular bill cost;
+}
+//This function will return bill amount for a premimum customer;
+double premiumBill(double minDay, double minNight)
+{
+    double cost,costDay,costNight;
+    //if total time spent in day is less than equal 75 minutes than it's free of cost
+    //only premimum bill charge have to pay;
+    if (minDay <= 75)
+        minDay = 0;
+    else    //else first 75 minutes is free and after 75 minutes for each minute 0.1 will be charged;
+        minDay -= 75;
+    costDay = 0.10 * minDay;
+    //if total time spent in night is less than equal 100 minutes than it's free of cost
+    //only premimum bill charge have to pay;
+    if (minNight <= 100)
+        minNight = 0;
+    else    //else first 100 minutes is free and after 75 minutes for each minute 0.05 will be charged;
+        minNight -= 100;
+    costNight = 0.05 * minNight;
+    cost = 25 + costDay + costNight;
+    return cost;    //return premimum bill cost;
+}
+int main()
+{
+    char service;
+    long long int accnum;
+    double cost;
+    cout << "Enter account number:: ";
+    cin >> accnum;  //account number of the customer;
+    cout << "Enter ('r' or 'R') for regular service or ('p' or 'P') for premium service:: ";
+    cin >> service; //type of the customer;
+    cout << fixed << showpoint << setprecision(2);
+    //'if' condition will execute is the customer is regular;
+    if (service == 'r' || service == 'R')
+    {
+        double minutes;
+        cout << "Enter the number of minutes used:: ";
+        cin >> minutes; //total no minutes the customer spent;
+        cost = regularBill(minutes);
+        cout << "Cost: $ " << cost << endl;
+    }
+    //'else if' condition will execute if the customer is premimum;
+    else if (service == 'p' || service == 'P')
+    {
+        double minDay, minNight;
+        double costDay, costNight;
+        cout << "Enter the number of minutes used at day and at night (separated by spaces):: ";
+        cin >> minDay >> minNight;  //total no of minutes the customer spent in day and night;
+        cost = premiumBill(minDay, minNight);
+        cout << "Cost: $ " << cost << endl;
+    }
+    //this code will execute for wrong key press;
+    else
+        cout << "Incorrect input. Try again later::" << endl;
+    return 0;
+}