math program

[ohfinite]

Im trying to write a program to allow a grade to be entered then present a math problem of varying difficulty. The higher the grade the harder the problems are. First grade is only addition, but second is addition and subtraction. I am completely spacing on how to set up my code to make the number being subtracted from be on top.

#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: ";
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 << left;
cout <<"Answer: ";
cin >> userAnswer;
}
else if (grade == 2) {
a = rand() % 89 + 10;
a = rand() % 89 + 10;}

}

Here is my code so far. I havent completed the second if yet because I dont know how to word it. Yes, this is a homework assignment, but I am not looking for a complete solution, only a push in the right direction. Like i said i need to allow for either addition or subtraction with the higher number being above the lower. Am i right in using if statements? Or should I be using switch or some other function? New to programming this semester, and our teacher is not very good. Thanks for any help you can give.