"If" problem

Question

#include <iostream>

using namespace std;

int main()
{
int grade;
cout << "Enter your grade\n";
cin >> grade;
if (grade<=100 && grade >=0) {
if (grade<=100 && grade>=94) { cout << "Your grade is A";};
if (grade<=93 && grade>=90) { cout << "Your grade is A-";};
if (grade<=89 && grade>=87) { cout << "Your grade is B+";};
if (grade<=86 && grade>=83) { cout << "Your grade is B";};
if (grade<=82 && grade>=80) { cout << "Your grade is B-";};
if (grade<=79 && grade>=77) { cout << "Your grade is C+";};
if (grade<=76 && grade>=73) { cout << "Your grade is C";};
if (grade<=72 && grade>=70) { cout << "Your grade is C-";};
if (grade<=69 && grade>=67) { cout << "Your grade is D+";};
if (grade<=66 && grade>=60) { cout << "Your grade is D";};
if (grade<=59 && grade>=0) { cout << "Your grade is F";};
} else {cout << "ENTER NUMBERS FROM 0-100";}
return 0;
}

when I input letters (f.e: ab) it outputs Your grade is F
I wanted it to output ENTER NUMBERS FROM 0-100

What's the problem?

Answer 1

and why when I open .exe file
I input but after closes immediately.

Answer 2

Thank you. As I understood , I should’ve been define string also?

Answer 3

My question is that my program should output my grade if I will input the numbers 0-100, BUT if i will write any character or numbers other than 0-100, it should output ENTER NUMBERS BETWEEN 0-100