Need help with a newbie project!

Hey guys, I just finished my gen ed stuff and have started my first programming class for my CS degree. Anyways, this is the second project I was assigned.

create a program that asks the user how the service was. Depending on answer use one of two tip rates. Calculate the total cost of their meal with tip included. Make sure cost is between 0 or 1000

Professor was super insistent on us using constants

Don't know (at the moment) how to restart something when you enter something that doesn't work - so I have to tell the user to restart


My problem is this: after the cin fetches a 'y' or 'n', if the user typed something like 'yes', the 'es' is then sent to the next cin, which doesn't know how to react to letters.

Need a way to prevent the first cin from taking answer bigger than y or n and I need a way to make it so that the second cin (which gets mealcost) to not accept letters.

Code:

Code:

---

#include <iostream>
#include <iomanip>

using namespace std;

const float TIP20=.20;
const float TIP15=.15;
const int MAXCOST = 1000;


int main() {
char service;
float tiprate, mealcost, total, tiptotal;

cout << setprecision(2) << fixed << showpoint;

cout << "Was the service tonight satisfactory?" << endl;
cin >> service;
if (service == 'y' || service == 'Y') tiprate = TIP20;
    else if (service == 'n' || service == 'N') tiprate = TIP15;
        else {
            cout << "Please enter a y or n and try again!" << endl;
            return 1;
            }
sleep(2);

cout << "Thank you for your feedback. Please enter the cost of your meal tonight" << endl;

cin >> mealcost;

if (mealcost < 0 || mealcost > MAXCOST ) {
    cout << "Error: You may only enter a number between 0 and 1000. Please try again." << endl;
    return 1;
    }

tiptotal = (tiprate * mealcost);
total = (mealcost + tiptotal);

cout << "Your meal cost was " << mealcost << "$" << endl;
cout << "Your tip was " << tiptotal << "$" <<  endl;
cout << "The total cost of your meal with tip tonight is " << "$" <<  total << endl;

return 0;
}

---

thanks!

I would suggest you:

• take a loop at loops for repeating stuff when answer is non-satisfactory.
• indent properly.
• read in a string (eg std::string) and compare it to your expected answers; it's clean and easy.
• don't use sleep; it's non-standard.

Code:

---

cin >> service;
if (service == 'y' || service == 'Y') tiprate = TIP20;
    else if (service == 'n' || service == 'N') tiprate = TIP15;
        else {
            cout << "Please enter a y or n and try again!" << endl;
            return 1;
            }

---

Would recommend that you use to toupper() on the input variable to obviate the need for multiple comparisons for the two cases.

Also, when you read into a char variable, you are actually taking two characters into the standard input buffer, the character entered and the newline character generated by hitting the enter key. You need to remove that newline character. As a simple (but not wholly correct) solution, try adding a cin.ignore() after you read into your char variable.

EDIT: For more detailed info, see this thread.

Quote:

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Originally Posted by rags_to_riches

Code:

---

cin >> service;

if (service == 'y' || service == 'Y') tiprate = TIP20;
    else if (service == 'n' || service == 'N') tiprate = TIP15;
        else {
            cout << "Please enter a y or n and try again!" << endl;
            return 1;
            }

---

Would recommend that you use to toupper() on the input variable to obviate the need for multiple comparisons for the two cases.

Also, when you read into a char variable, you are actually taking two characters into the standard input buffer, the character entered and the newline character generated by hitting the enter key. You need to remove that newline character. As a simple (but not wholly correct) solution, try adding a cin.ignore() after you read into your char variable.

EDIT: For more detailed info, see this thread.

---

Thanks for the post. The cin.ignore() trick worked for eliminating one character, so a phrase like 'ya' or 'no' would be remedied. However, 3 or more characters is still a problem. 'Yes', for example, still caused the error.

Also, on the example of toupper, I went to the page you linked and it seemed pretty useful, but I still am not quite sure how to use it (especially in the case of my code). The example they provided had some things I have never seen before, and so it kinda confused me.

I believe that thread tells you how to use cin.ignore() to ignore more than 1 character, if I read it correctly.

istream::ignore - C++ Reference

This also, but if you're too lazy to click on his forum link, you're probably too lazy to click on this one as well :x

Quote:

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Originally Posted by Rodaxoleaux

I believe that thread tells you how to use cin.ignore() to ignore more than 1 character, if I read it correctly.

istream::ignore - C++ Reference

This also, but if you're too lazy to click on his forum link, you're probably too lazy to click on this one as well :x

---

not sure why you said that??? I did click on those links he posted, but if there was an example to do more stuff then I clearly didn't understand it.....I have only been in this intro c++ course for like 4 weeks. I don't understand a lot of the syntax I see posted in those links, especially the official ones on sites like cplusplus.

I will look again, but like I said, if it contains a lot of syntax I don't understand...it isn't much use to me. I was HOPING someone here would take the time to explain one of the two things I needed. Though if that is too much to ask, then maybe you could redirect me to a forum that would be able to explain these things to me?

I don't want to sound helpless here, but most of the suggestions I have seen thus far (aside from the cin.ignore one) were really above my level. I said in the title I was a newbie, so some kind of context would be nice with these suggestions.

Code:

---

while (!cin.good())
  {
      cin.clear();
      cin.ignore(numeric_limits<streamsize>::max(), '\n');
      cout << "enter anything (choose a number to stop): ";
      cin >> omgnumbers;

---

For example, I just learned about the loop functions today. Specifically while. A lot of the stuff here is tough for me to understand, and thus would be kind of hard for me to implement.

I have never seen cin.good or cin.bad.

(numic_limits<streamsize>::max(), '/n')

I have zero idea what this is about.

Code:

---

/* toupper example */
#include <stdio.h>
#include <ctype.h>
int main ()
{
  int i=0;
  char str[]="Test String.\n";
  char c;
  while (str[i])
  {
    c=str[i];
    putchar (toupper(c));
    i++;
  }
  return 0;
}

---

I have never used putchar before. Not sure what while(str[i]) does/means.

why is i++ there?

Take it slow.
If you've just learnt about loops, you do not need to know the intricate details of how numeric_limits work.
Just know that

Code:

---

cin.ignore(numeric_limits<streamsize>::max(), '\n');

---

Ignores (discards) the maximum possible number of characters from the standard input stream until a newline is reached.

If you take a look at what I posted earlier:

Quote:

---

Originally Posted by Elysia

• read in a string (eg std::string) and compare it to your expected answers; it's clean and easy.

---

You will find a solution that's very easy and doesn't involve you having to understand or know how ignore or numeric_limits work at all.
Eg:

Code:

---

std::string answer;
std::cout << "Your anwer: ";
std::getline(answer, std::cin);
while (answer != "yes" && answer != "no")
{
        std::cout << "\nInvalid answer. Please answer with \"yes\" or \"no\": ";
        std::getline(answer, std::cin);
}

---

Quote:

---

Originally Posted by Elysia

If you take a look at what I posted earlier:

You will find a solution that's very easy and doesn't involve you having to understand or know how ignore or numeric_limits work at all.
Eg:

Code:

---

std::string answer;
std::cout << "Your anwer: ";
std::getline(answer, std::cin);
while (answer != "yes" && answer != "no")
{
    std::cout << "\nInvalid answer. Please answer with \"yes\" or \"no\": ";
    std::getline(answer, std::cin);
}

---

---

seems useful, but I am not sure what std:: stuff does.

Is the '::' some universal syntax used? If so, what does it do exactly? What is the standard (std) stand for too? Or rather, what does it do.

:: references a member of a namespace or the static members of structs and classes.

std is the standard namespace that all standard library stuff lies in.

Ahh. So when I see std::cout, you are using a different cout than if you had just typed like

cout << "Your answer" ;

What is the difference between them if there is one?

There is no difference. There is only one cout and it lies in the std namespace.
However, many books and programmers use

using namespace std;

which essentially tells the compiler: if you can't find this symbol in the global namespace (ie no namespace at all), then look in the std namespace.
So when you type cout, the compiler searches for ::cout (global namespace), then std::cout.
I simply like being explicit since the using namespace statements has its disadvantages.

Quote:

---

Originally Posted by Elysia

I simply like being explicit since the using namespace statements has its disadvantages.

---

Yeah, such as defeating the whole purpose of having namespaces in the first instance.

Quote:

---

Originally Posted by Elysia

There is no difference. There is only one cout and it lies in the std namespace.

---

There is only one cout, one std namespace and one language. All other false idol languages will answer to the almighty universal compiler when runtime comes.

Quote:

---

Originally Posted by Elysia

using namespace std;

which essentially tells the compiler: if you can't find this symbol in the global namespace (ie no namespace at all), then look in the std namespace.
So when you type cout, the compiler searches for ::cout (global namespace), then std::cout.

---

Not quite: it depends on where the using directive is placed. Furthermore, I do not think the "the compiler searches for ::cout (global namespace), then std::cout". Rather, if ::cout also existed, there would be a name collision resulting in an ambiguity that can only be resolved by either removing the using directive or fully qualifying the names.

Wow, I see. That makes sense. Thanks for the explanation.

Does not including something like

Code:

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using namespace std;

---

initially have some kind of advantage? (Something beyond me maybe? Like memory management or something.....)

It reduces the risks for namespace collision. That is, ambiguity where the compiler cannot decide upon if you meant, say, ::foo, or bar::foo.
For example, use the "using namespace std" and then declare a min or max function that takes two ints and returns an int. Then call that. It demonstrates very well the disadvantages of namespace directives.

Quote:

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Originally Posted by Eep

Does not including something like

Code:

---

using namespace std;

---

initially have some kind of advantage?

---

Yes, the advantage is that you don't have to qualify names in the std namespace, which can make code both easier to read and write when many names in the std namespace are used. However, if you are using names that are also in the std namespace and/or have other using directives, then your code could end up easier to write but harder to read because of the possibility of name collision.