Recipe to nutrition converter - c++

Question

I have the whole thing ready to go, but I'm down to one problem, my professor wants us to ask the user to put in how many servings there will be, my problem is here:
string recipeName, userInputStr, servingNumber;
int userInputInt;
double totalCals, totalCarbs;
// initialize accumlator variables
totalCals = 0.;
totalCarbs = 0;
// asking for name of recipe and number of servings
cout << "What is the name of your recipe? ";
getline(cin, recipeName);
cout << "How many servings would you like? ";
getline(cin, servingNumber);
istringstream(servingNumber) >> totalCals, totalCarbs;
if (servingNumber<1 || servingNumber>10)
{
cout << "You have entered the wrong answer. " << endl;
return 0;
}
more specifically, it's here:
if (servingNumber<1 || servingNumber>10)
I keep getting an error on the < and > saying "no operator matches these operands"
I was told I'm supposed to convert the string servingNumber to int then compare it, but isn't it converted here?:
istringstream(servingNumber) >> totalCals, totalCarbs;
and then compared on the if statement?
I'm not sure what I'm doing wrong..

Answer 1

You declared those variables as strings, but when you compare them to integer, no overloads exists that take those arguments, and there is no acceptable conversion. I think you meant for them to be integers:
string recipeNamem userInputStr;
int servingNumber; /*
^^^
You also don't need the istringstream either.
Also, instead of getline(cin, servingNumber), do cin >> servingNumber.

Answer 2

You are defining servingNumber as a string in your code. You do not compare a string with numbers, the operator is not defined for the string class.

Answer 3

You're getting this error because you're trying to compare a string with a number in your if statement. Beyond that there are some other things with this code that might be worth looking at.
The first is the way you define variables. In C the idiom was to define all the variables at the top of your function as you're doing here. However in C++ we prefer to define variables where they are used. The goal is to reduce the amount of thinking you need to do on a chunk of code:
string recipeName;
cout << "What is the name of your recipe?";
getline(cin, recipeName);
string servingNumber;
double totalCals;
double totalCarbs;
getline(cin, servingNumber);
istringstream(servingNumber) >> totalCals, totalCarbs;
if( servingNumber < 1 || servingNumber > 10)
{
cout << "You have entered the wrong answer. " << endl;
}
The next issue is that istringstream(servingNumber) >> totalCals, totalCarbs; doesn't do what you think it does. I don't know how you're planning to use totalCals and totalCarbs but right now this line only sets totalCals and does nothing to totalCarbs.
Finally your major issue is that you're trying to compare servingNumber (a string) to a raw integer. We need to convert servingNumber to an integer. Some people have recommended atoi which will do the job but is often considered unidiomatic C++. Since you're already using stringstream we can use that to convert our number like so:
string recipeName;
cout << "What is the name of your recipe?";
getline(cin, recipeName);
string servingNumberInput;
double totalCals;
double totalCarbs;
getline(cin, servingNumberInput);
istringstream(servingNumberInput) >> totalCals, totalCarbs;
int servingNumber;
istringstream(servingNumberInput) >> servingNumber;
if( servingNumber < 1 || servingNumber > 10)
{
cout << "You have entered the wrong answer. " << endl;
}
Alternatively if you're not depending on getline you can just stream the number directly in from cin like so:
string recipeName;
cout << "What is the name of your recipe?";
getline(cin, recipeName);
int servingNumber;
cin >> servingNumber;
if( servingNumber < 1 || servingNumber > 10)
{
cout << "You have entered the wrong answer. " << endl;
}
I got rid of the totalCarbs and totalCals stuff because we don't have any idea what they're doing at the moment.