best way to print error and terminate

[ohfinite]

So I have written a math tutor program for first, second, and third graders. I used if/else statements for the whole thing and when i finally finish I read i need to add an appropriate error message and quit the program. Im wondering if there is a more intuitive way of doing this seeing as I have a bunch of if/else statements already and dont want to add another. Here is the beginning of my code, the only relevant part to this question.

#include <iostream>
#include <string>
#include <cstdlib>
#include <ctime>
#include <iomanip>
#include <cmath>
using namespace std;

string name;
int grade;
double a, b, c;
double userAnswer;
int main()
{
unsigned seed = time(0);
srand(seed);

cout <<"Welcome to the Math Tutor\n\n";

cout <<"Enter your name: ";
getline(cin, name);
cout <<"Enter your grade (1, 2, or 3): ";
cin >> grade;


cout <<"\nPlease answer the following problem "<< name <<".\n"<< endl;

if(grade == 1){
a = rand() % 10;
b = rand() % 10;
c = a + b;
cout <<"Problem: ";
cout << right << setw(5);
cout << a << endl;
cout << right << setw(13);
cout <<"+ " << b << endl;
cout << right << setw(14);
cout <<"----"<< endl;
cout << "Answer: ";
Etc. I have 2 other if statements for if grade is equal to 2 or 3. I need to put the error message after the cin >> grade; and terminate the program provided the input isn't one of the choices. Like I said I would just like to know if there is a more intuitive way to do those two things. Im a newbie to c++ and can't see it or havent been taught it yet. Thanks for any help.

[bingo1]

Yes, there are a few more ways to do what you want.

But based on what you have, I would try to use an if-else statement.

Here's how it works:

if (//some condition here){
    //some code here.....
}


else{
    //If the the if-statement above is true and runs, then the else will not. 
//If the if-statement above is false and does not run, then the else will.
}

So in your case, I would try:

if (grade > 3)//If grade is greater than 3...
{
//output message here.
}

else{

//all the options for 1, 2, and 3 would go here.

}

It's not the best solution, but it works.

And this is sort of off-topic, but you should try not to use global variables so much. It can be a bad habit to develop.

[ohfinite]

I suppose I'll just stick with that then. Only reason I didnt want to do that was because I didnt want to bury 150 lines of code into that else. And using those globals were how we were taught to do this assignment. Im sure I will stray from them as I progress in class and gain experience.

[ohfinite]

I guess another problem I have with that assignment is what if they enter a zero, or anything else. You see why I am looking for a more intuitive way? Will that assignment cover all the bases? ultimately what I'm looking for. Thanks for the reply though

[bingo1]

Sry about late reply:

What if they enter a zero? You can try something like this:

//This says if grade is greater than 3, OR if grade is less than 1, 
//then the if-statement will execute.
//Zero will trigger the if-statement. So will -1, -2, 4, 5, etc...
if (grade > 3 || grade < 1){
//code goes here...
}


else{
//...
}

Using if-else statements are generally very inefficient. So don't worry too much about sticking 150 lines into the else. You'll learn how to organize things more efficiently very soon.

[TwilightSpectre]

If you are in your main() statement, you can normally end it by simply returning early. Alternately, you can use cstdlib's exit() or abort() functions.
For example:

#include <cstdlib>

// ...

if (grade > 3 || grade < 1) {
    // Error printing code here
    // If in main():
    return 1;       // Return an error code to the OS

        // Otherwise, you could do this:
    abort();        // Ends the program immediately, without cleaning data
        // OR, in less extreme cases:
    exit(1);        // Ends the program normally, as if
                    // you called return 1 in main.   

}

// Rest of code goes here 

EDIT:
Another option is to use std::terminate() in #incude <exception> , though from memory that just calls abort() anyway.

[Smac89]

try {
        //some code here...
}

catch (/*Some exception name here...*/) {
        //Do something with the exception or terminate
}