Grading system in C++

问题:

So this is my C++ question :

Write a program that translates a letter grade into a number grade. Letter grades are A, B, C, D and F, possibly followed by + or -. Their numeric values are 4, 3, 2, 1 and 0. There is no F+ or F-. A + increases the numeric value by 0.3, a – decreases it by 0.3. However, an A+ has value 4.0.

Enter a letter grade: B
The numeric value is 2.7

And here is my code :

int main ()
{
    char grade;
    int value;
    cout << "Enter letter grade : " ;
    cin >> grade;

    switch(grade)
    {
    case 'A' : value = 4;
        break;
    case 'B' : value =  3;
        break;
    case 'C' : value = 2;
        break;
    case 'D' : value = 1;
        break;
    case 'E' : value = 0;
        break;
    default : cout << "Wrong input " << endl;
        break;
    }

    cout << value;
    system("PAUSE");
    return 0;
}

It able to print out 4 for A, 3 for B and so on. But however, the question required us to make the calculation for the + and - also. Am I supposed to use if else statement after the switch?

回答1:

If the input is A+ or B-, then it is not a character anymore. So, get it using a string of chars, and check the values.

char a[3];
float m,n;
cin>>a;
if(a[1]=='+')
   m=0.3;
else if (a[1]=='-')
   m=-0.3;
else
    m=0;
switch(a[0])
{
  //Assign the value of n as 4,3,2,1 depending upon the grade.
}
cout<<n+m;

will print the grade

回答2:

I'd deal with each character in turn. You know that the first one should be a letter grade, so you look at that one first, and you could just use a switch statement like you've already got for that.

uint value = 0;
char grade_letter = grade[0];

switch (grade_letter) {
    // assign value as appropriate
}

Then, if the second character exists, check if it's a + or a - and modify the value you got from the switch statement accordingly.

if (grade.length() > 1) {
    char modifier = grade[1];
    switch (modifier) {
        case '+': value += 0.3;
        // etc.
    }
}

Before all that of course, you'll want to check for the special case of A+ and skip everything else.

An alternative approach would be to replace the switch statements with lookups in a previously-prepared data structure, something like a std::map<char, int>, which, even if the initialisation code prepared it from hardcoded data, would open the way to loading the grade information from a configuration file or database at some point in the future. Special-casing A+ in that case becomes slightly trickier though.

回答3:

Simply adding more cases would help. Modifying your code as below:

    int main ()
    {
    String grade;
    float value;
    cout << "Enter letter grade : " ;
    cin >> grade;

    switch(grade)
    {
    case "A" : value = 4;
        break;
    case "A+" : value = 4.3;
        break;
    case "A-" : value = 3.7;
        break;
    case "B" : value = 3;
        break;
    case "B+" : value = 3.3;
        break;
    case "B-" : value = 2.7;
        break;        
    case "C" : value = 2;
        break;
    case "C+" : value = 2.3;
        break;
    case "C-" : value = 1.7;
        break;        
    case "D" : value = 1;
        break;
    case "D+" : value = 1.3;
        break;
    case "D-" : value = 0.7;
        break;        
    case "F" : value = 0;
        break;
    default : cout << "Wrong input " << endl;
        break;
    }

    cout << value;
    system("PAUSE");
    return 0;

    }

This is a straightforward extension of what you did, there can be million other ways.