Question

I've built a C++ program that calculates the user's class average based on three test. Can somebody show me how to get the program to look for invalid input?

#include <iostream>

#include <string>

#include <iomanip>

using namespace std;

int main()

{

//variables

int score_1; //test 1 input from user

int score_2; //test 2 input from user

int score_3; //test 3 input from user

int highest; // the higher score of test 1 & 2

int course_average; //average for class

//Introduce user to program

cout << "Welcome to the grade calculator. You will enter three test scores\n";

cout << "The highest of the first two grades and the third grade will be added together\n";

cout << "to determine the numeric grade average for the course.\n";

cout << "Each test score has a maximum of 50 points.\n\n";

//request input from user

cout << "Enter first test score: ";

cin >> score_1;

cout << "Enter second test score: ";

cin >> score_2;

cout << "Enter third test score: ";

cin >> score_3;

// test to see if user input is valid.

//Calculate numerical average for class

{

if (score_1 > score_2)

(highest = score_1);

else if

(highest = score_2);

}

cout << int(course_average = highest + score_3);

cout << " is your course average. \n";

//define range for letter grade

if ((course_average >= 90) && (course_average < 100))

{

cout << "The letter grade is: " << "A";

}

else if ((course_average >= 80) && (course_average < 90))

{

cout << "The letter grade is: " << "B";

}

else if ((course_average >= 70) && (course_average < 80))

{

cout << "The letter grade is: " << "C";

}

else if ((course_average >= 60) && (course_average < 70))

{

cout << "The letter grade is: " << "D";

}

else if ((course_average >= 50) && (course_average <= 0))

{

cout << "The letter grade is: " << "F";

}

}

Answer 1

Screenshot

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Program

//Header files
#include <iostream>
#include <string>
#include <iomanip>
using namespace std;
//Main method
int main(){
   //variables
   int score_1; //test 1 input from user
   int score_2; //test 2 input from user
   int score_3; //test 3 input from user
   int highest; // the higher score of test 1 & 2
   int course_average; //average for class
   //Introduce user to program
   cout << "Welcome to the grade calculator. You will enter three test scores\n";
   cout << "The highest of the first two grades and the third grade will be added together\n";
   cout << "to determine the numeric grade average for the course.\n";
   cout << "Each test score has a maximum of 50 points.\n\n";
   //request input from user
   cout << "Enter first test score: ";
   cin >> score_1;
   while (score_1 < 0 || score_1>100) {
       cout << "ERROR!!!score should be within 0-100!!!" << endl;
       cout << "Enter first test score: ";
       cin >> score_1;
   }
   cout << "Enter second test score: ";
   cin >> score_2;
   while (score_2 < 0 || score_2>100) {
       cout << "ERROR!!!score should be within 0-100!!!" << endl;
       cout << "Enter second test score: ";
       cin >> score_2;
   }
   cout << "Enter third test score: ";
   cin >> score_3;
   while (score_3 < 0 || score_3>100) {
       cout << "ERROR!!!score should be within 0-100!!!" << endl;
       cout << "Enter third test score: ";
       cin >> score_3;
   }
   // test to see if user input is valid.
   if(score_1>=0 && score_2>=0 && score_3>=0 && score_1<=100 && score_2 <=100 && score_3 <= 100)
   {
       //Calculate numerical average for class
       if (score_1 > score_2)

           (highest = score_1);

       else if

           (highest = score_2);

   }
   else {
       cout << "Entered Scores wrong!!!" << endl;
       exit(0);
   }

   cout << int(course_average =( highest + score_3)/2);

   cout << " is your course average. \n";

   //define range for letter grade

   if ((course_average >= 90) && (course_average < 100))

   {

       cout << "The letter grade is: " << "A";

   }

   else if ((course_average >= 80) && (course_average < 90))

   {

       cout << "The letter grade is: " << "B";

   }

   else if ((course_average >= 70) && (course_average < 80))

   {

       cout << "The letter grade is: " << "C";

   }

   else if ((course_average >= 60) && (course_average < 70))

   {

       cout << "The letter grade is: " << "D";

   }

   else if ((course_average >= 50) && (course_average <= 0))

   {

       cout << "The letter grade is: " << "F";

   }

}

-------------------------------------------------

Output

Welcome to the grade calculator. You will enter three test scores
The highest of the first two grades and the third grade will be added together
to determine the numeric grade average for the course.
Each test score has a maximum of 50 points.

Enter first test score: 68
Enter second test score: 75
Enter third test score: 75
75 is your course average.
The letter grade is: C

----------------------------------------------

Note

I assume you want input error check this way, if you want to re-enter if error occur ,then we have to check after each input