Write a C++ program to determine a student's grade. It reads three test scores (between 0 and 100) and calculates the

average score and converts it to a letter grade.

Grade Conversion Rules:

rule a. If the average score is 90 or more the grade is 'A'.

rule b. If the average score is 70 or more and less than 90 then check the third test score. If the third score is 90 or more

the grade is 'A' otherwise the grade is 'B'.

rule c. If the average score is 50 or more and less than 70 then check the average of the second and third scores. If the

average of the last two is 70 or more, the grade is 'C' otherwise it is a 'D'

rule d. If the average score is less than 50 then the grade is 'F'.

Rounding Rule: Midpoint Rounding

Calculate the grade average as a double. Round up to the next int if the fractional part is .5 or greater, otherwise

truncate the fraction by casting to an int.

The algorithm is: Add .5 to the average and cast the result to an int.

Example: average = (int)(average+0.5);

```
#include <iostream>
#include <iomanip>
using namespace std;
int main()
{
//variable declarations
double t1, t2, t3, avg;
//Input
cout << "Enter in three test grades that the sudent received:\n";
cin >> t1, t2, t3;
//Process
avg = (t1 + t2 + t3) / 3;
//Output
if (avg >= 0)
{
if (avg >=90)
{
cout << "The student's average is an A:\n" << avg << endl;
}
else if (70 <= avg >= 89)
{
cout << "The student's average is a B:\n" << avg << endl;
}
else if (50 <= avg >= 69)
{
cout << "The student's average is a C:\n" << avg << endl;
}
else (avg <= 49)
{
cout << "The student's average is a F:\n" << avg << endl;
}
}
else
cout << "The test scores cannot be less than 0. Please enter 0 or more." << endl;
system("pause");
return 0;
}
```

I need help. At this point, I do not know what I am doing. I can guess that my if statements are screwed, but I don't know how to fix them.

Please help.

Thank you.