function returning something strange - c++

Question

I have a function to get a grade point value from a grade object and return it as a double as implemented below:
double Grade::getNumGrade()
{
double value;
if (strGrade == "A")
{
return 4.0;
}
else if (strGrade == "A-")
{
return 3.7;
}
else if (strGrade == "B+")
{
return 3.3;
}
else if (strGrade == "B")
{
return 3.0;
}
else if (strGrade == "B-")
{
return 2.7;
}
else if (strGrade == "C+")
{
return 2.3;
}
else if (strGrade == "C")
{
return 2.0;
}
else if (strGrade == "C-")
{
return 1.7;
}
else if (strGrade == "D+")
{
return 1.3;
}
else if (strGrade == "D")
{
return 1.0;
}
else if (strGrade == "D-")
{
return 0.7;
}
else if (strGrade == "F")
{
return 0.0;
}
}
With strGrade being the string representation of the grade. However with the code here:
Grade jon = Grade("A+");
cout << jon.getNumGrade();
outputs :
-1.#IND
The constructor just makes sure the first letter is uppercase and then saves the string provided as strGrade. Not sure why this is happening or how to fix it?

Answer 1

As NathanOliver pointed out,
You never handle A+ in your if statements.
See
double value;
if (strGrade == "A")
{
return 4.0;
}
else if (strGrade == "A-")
{
return 3.7;
}
No conditional for when strGrade == A+.
But since this was answered in a comment, I'll attempt to justify writing this as an answer by giving you some advice.
Your final conditional,
else if (strGrade == "F")
{
return 0.0;
}
shouldn't be an else if. There's plenty of good ways to deal with error handling (like an unexpected input) but a very easy yet efficient practice is to end your conditionals with an else. For example,
//if all other conditionals thus far have returned false
else
{
... error handling here ...
}
In the event that you fall into this else, log an error and/or gracefully exit the program; at the least, return a value and handle it appropriately.
Also consider applying your if else in a logical ordered based on the likelihood of a certain conditional being evaluated to true. More specifically, if you know that a majority of students are going to get a B+, make that the first expression that gets evaluated in your if else series. If a B- is the next most common grade, make that the second expression that gets evaluated; and so on. Additionally, if you know that a grade is least likely to be passed through, make that the last conditional you check.

Answer 2

Not sure why this is happening or how to fix it?
That's happening because your function doesn't return a value for the "A+" case and exposes undefined behavior.
As mentioned in comments you should have seen a compiler warning about that stating
Not all of your code paths return a value.
You can fix that providing always a (reasonable) return value before your last brace in the function, or throwing an exception for unexpected cases of strGrade.
BTW the much easier solution would be to use a std::map<std::string,double> to hold the associative values:
double Grade::getNumGrade() {
static std::map<std::string,double> numGrades = {
{ "A", 4.0 } ,
{ "A-", 3.7 } ,
{ "B+", 3.3 } ,
// ...
};
auto found = numGrades.find(strGrade);
if(found != numGrades.end()) {
return found->second;
}
return 0.0;
}
It also looks that this should be a free or static function rather than a class member function:
double getNumGrade(const std::string& strGrade) {