Calculate price of a phone call

Hello everyone, I am new to this forum and am looking for some assistance, any help would be greatly appreciated! I'm trying to calculate the price for a phone call under these requirements,
 Price per min 4 dollars.
 VAT 25%.
 Between 8:00 and 18:30 you pay full price
 Prior to 8:00, and after 18:30 are given 65% discount on price per min.
 For conversations longer than 30 minutes are given a discount of 15% of the total price.

There is something wrong with my calculations but I can't figure out what it is.

Here is some examples for prices if the calculations work as they should,
07:45 - 8:15 ---> 101.25 $
07:45 - 8:16 ---> 90,31 $
07:30 - 07:38 ---> 14,00 $
07:55 - 08:10 ---> 58,75 $
12:03 - 12:53 ---> 212,50 $
17:58 - 18:37 ---> 146,41 $
07:59 - 18:31 ---> 2680,48 $

Code:

---

#include <iostream>
#include <string>
#include <sstream>
#include <iomanip>

using namespace std;

double convert(string start, string end);
double priceCalc(int startHour, int startMinute, int endHour, int endMinute);
bool errorCheck(int startHour, int startMinute, int endHour, int endMinute);

int main()
{
    char ch;
   
    do
    {
        string callStart,callEnd;
       
        cout<<"What time the call start? (hh:mm): ";
        getline(cin, callStart);
       
        cout<<"What time did the call end? (hh:mm): ";
        getline(cin, callEnd);
       
        cout<<convert(callStart,callEnd)<<" $" << endl;
       
        cout << "Run again(y/n)? ";
        cin >> ch; cin.ignore(250,'\n');
       
        do
        {
            ch = toupper(ch);
        }while( !(ch == 'Y' || ch == 'N'));
       
    }while(ch == 'Y');
   
    return 0;
}


double convert(string start, string end)
{
    int startHour = 0, startMinute = 0, endHour = 0, endMinute = 0;
   
    string::size_type startPos = start.find(":");
    if(startPos != string::npos)
        ;
    else
    {
        cout << "Only : is allowed" << endl;
        return 0;
    }
   
    string::size_type endPos = end.find(":");
    if(endPos != string::npos)
        ;
    else
    {
        cout << "Only : is allowed" << endl;
        return 0;
    }
   
    start.replace(start.find(":"), 1, " ");
    end.replace(end.find(":"), 1, " ");
   
   
    istringstream iss(start);
    iss >> startHour >> startMinute;
   
    iss.clear();
    iss.str(end);
    iss >> endHour >> endMinute;
   
    if (errorCheck(startHour,startMinute,endHour,endMinute))
        return 0;
   
    return priceCalc(startHour,startMinute,endHour,endMinute);
   
}


bool errorCheck(int startHour, int startMinute, int endHour, int endMinute)
{
   
    if (((startHour * 60) + startMinute) >= ((endHour * 60) + endMinute))
    {
        cout << "Time error ";
        return true;
    }
   
    if (startHour>23||startHour<00||endHour>23||endHour<00||startMinute>59||startMinute<00||endMinute>59||endMinute<00)
    {
        cout << "Time error ";
        return true;
    }
    else
        return false;
}


double priceCalc(int startHour, int startMinute, int endHour, int endMinute)
{
    int startinMiuntes = startHour * 60 + startMinute;
    int endinMinutes = endHour * 60 + endMinute;
   
   
    int totMin = 0;
    int const pricePerMin=4;
    double price;
    const double VAT=1.25;
    const double disconut=0.35;
    const double discount30min=0.85;
   
    totMin=endinMinutes-startinMiuntes;
   
    if((startHour>=8 && startMinute>=0) && (endHour<=18 && endMinute<=30))
        price=totMin*pricePerMin*VAT;
    else
        price=(pricePerMin*disconut)*totMin*VAT;
   
    if(totMin>30)
    {
        price=price*discount30min;
    }
   
    return price;
}

---

Code:

---

do
        {
            ch = toupper(ch);
        }while( !(ch == 'Y' || ch == 'N'));

---

Don't you want to input ch again within this loop?

Code:

---

if(startPos != string::npos)
        ;
    else
    {
        cout << "Only : is allowed" << endl;
        return 0;
    }

---

This can be simplified as

Code:

---

if (startPos == string::npos)
{
    cout << "Only : is allowed" << endl;
    return 0;
}

---

Code:

---

start.replace(start.find(":"), 1, " ");

---

As you already have the return value of .find() from previous code, why not just

Code:

---

start.replace(startPos, 1, " ");

---

Code:

---

if((startHour>=8 && startMinute>=0) && (endHour<=18 && endMinute<=30))

---

What happens if a phone call starts prior to 8 but finishes after 8? Doesn't the part of the call prior to 8 get a discount but the part after 8 but before 18:30 charged at full price?

With the first loop I want to ask the user if she/he want to run the program again. But it seems like I have done something wrong there as well because if I input something else than y or n.

Yes that's true! If the call starts before 8 and finish after 8 you get a discount on the part that's after 8.