C++ switch statement beginner exercise

Question

Can anyone please explain to me where is the error? I can't really understand😂

This is the exercise:

"Write a program that allows the user to enter the grade scored in a programming class (0-100). Modify the program so that it will notify the user of their letter grade using switch statement. 0-59 F 60-69 D 70-79 C 80-89 B 90-100 A."

And this is my code:

#include <iostream>
using namespace std;
int main()

{ int grade=0;

cin>>grade;

switch (grade)
{
case 50&&59:
cout<<"You've got a F";
break;
case 60&& 69:
cout<<"You've got a D";
break;
case 70&&79:
cout<<"Yuo've got a C";
break;
case 80&&89:
cout<<"Yuo've got a B";
break;
case 90&&99:
cout<<"Yuo've got an A";
break;
} return 0;
}

Answer 1

Switch as per the standards does not work for ranges.

A&&B is of type bool, and bool variables can hold either a true or a false. These can be converted to a 1 or a 0. So your switch block translates to :

switch (grade)
{
case 1:
cout<<"You've got a F";
break;
case 1:
cout<<"You've got a D";
break;
case 1:
cout<<"Yuo've got a C";
break;
case 1:
cout<<"Yuo've got a B";
break;
case 1:
cout<<"Yuo've got an A";
break;
}

Since all the case values are the same, the compiler throws an error.

To solve this problem, use an if else-if ... else combination.

if(grade<=59&&grade>=50)
cout<<"You've got a F";
else if(grade<=69&&grade>=60)
cout<<"You've got a D";
// Other cases follow.
// Base case for the last option.
else cout<<"You've got an A";

If you have GNU GCC as your compiler, you can also use case ranges unique to GCC:

switch(grade)
{
case 50...59:
cout<<"You've got a F";
break;
// The rest of the cases follow.
}

Answer 2

#include <iostream>

using namespace std;

int main()
{
int marks;
cout<<"Enter your Marks: "<<endl;
cin>>marks;

switch(marks)
{
case 0:
case 1:
case 2:
case 3:
case 4:
case 5:
case 6:
case 7:
case 8:
case 9:
case 10:
case 11:
case 12:
case 13:
case 14:
case 15:
case 16:
case 17:
case 18:
case 19:
case 20:
case 21:
case 22:
case 23:
case 24:
case 25:
case 26:
case 27:
case 28:
case 29:
case 30:
case 31:
case 32:
case 33:
case 34:
case 35:
case 36:
case 37:
case 38:
case 39:
case 40:
case 41:
case 42:
case 43:
case 44:
case 45:
case 46:
case 47:
case 48:
case 49:
case 50:
case 51:
case 52:
case 53:
case 54:
case 55:
case 56:
case 57:
case 58:
case 59:
cout<<"Yuo've got an F";
break;
case 60:
case 61:
case 62:
case 63:
case 64:
case 65:
case 66:
case 67:
case 68:
case 69:
cout<<"Yuo've got an D";
break;
case 70:
case 71:
case 72:
case 73:
case 74:
case 75:
case 76:
case 77:
case 79:
cout<<"Yuo've got an C";
break;
case 80:
case 81:
case 82:
case 83:
case 84:
case 85:
case 86:
case 87:
case 88:
case 89:
cout<<"Yuo've got an B";
break;
case 90:
case 91:
case 92:
case 93:
case 94:
case 95:
case 96:
case 97:
case 98:
case 99:
case 100:
cout<<"Yuo've got an A";
break;

default:
cout<<"Invalid number"<<endl;
break;
}
return 0;
}