The result is not same as I expected - c++

Question

The answer that I want should be 88.5 but it turns out to be 3.60434e+006. I think there's no problem with my quotient formula. What should I do?
#include <iostream>
using namespace std;
int main()
{
int Grade_one, Grade_two;
int Average = Grade_one+Grade_two;
double average = Average/2;
cout<<"Please input your Grade No.1: ";
cin>>Grade_one;
cout<<"Please input your Grade No.2: ";
cin>>Grade_two;
if (Grade_one == Grade_two){
cout<<"Your Grades are Same."<< endl;
}
if(Grade_one >= 50 && Grade_two >= 50 && Grade_one <= 74 && Grade_two <= 74){
cout<<"Hey! You should focus on your study, your grade is concerningly LOW."<< endl;
}
else if(Grade_one <= 49 && Grade_two <= 49){
cout<<"DUDE! you will fail for sure if you don't study."<< endl;
}
else if(Grade_one >= 75 && Grade_two >= 75 && Grade_one <= 100 && Grade_two <= 100){
cout<<average <<endl;
}
return 0;
}
"result"
Please input your Grade No.1: 88
Please input your Grade No.2: 89
3.60434e+006
Process returned 0 (0x0) execution time : 3.238 s
Press any key to continue.
The answer should be 88.5. How should I fix this?

Answer 1

Grade_one and Grade_two undefined when you first use them. You also need to cast Average to double if you want the result to be double as well.
#include <iostream>
using namespace std;
int main()
{
int Grade_one, Grade_two;
cout<<"Please input your Grade No.1: ";
cin>>Grade_one;
cout<<"Please input your Grade No.2: ";
cin>>Grade_two;
int Average = Grade_one+Grade_two;
double average = (double)Average/2;
if (Grade_one == Grade_two){
cout<<"Your Grades are Same."<< endl;
}
if(Grade_one >= 50 && Grade_two >= 50 && Grade_one <= 74 && Grade_two <= 74){
cout<<"Hey! You should focus on your study, your grade is concerningly LOW."<< endl;
}
else if(Grade_one <= 49 && Grade_two <= 49){
cout<<"DUDE! you will fail for sure if you don't study."<< endl;
}
else if(Grade_one >= 75 && Grade_two >= 75 && Grade_one <= 100 && Grade_two <= 100){
cout<<average <<endl;
}
return 0;
}

Answer 2

int Grade_one, Grade_two;
int Average = Grade_one+Grade_two;
Here, you read uninitialized variables. This is Undefined Behaviour and everything could happen: a crash, trash data, weird behaviour, ...
You need to delay the use of a variable only after you set it to a useful value, e.g.:
int Grade_one, Grade_two;
cout<<"Please input your Grade No.1: ";
cin>>Grade_one;
cout<<"Please input your Grade No.2: ";
cin>>Grade_two;
int Average = Grade_one+Grade_two;
double average = Average/2;

Answer 3

You are calculating average before Grade_one and Grade_two are initialized, that cannot work (it is undefined behavior). If you want to define something now and execute it later thats a function. You can use a lambda expression here. Average is a misnomer, it is a sum, not an average. You are using integer arithmetics for the division, but to get correct result it has to be calculated with floating points. I think you got the conditions for the if right, but the last case is simpler if you just make it an else without the condition. Last but not least, you should initialize variables always:
#include <iostream>
using namespace std;
int main()
{
int Grade_one = 0;
int Grade_two = 0;
auto average = [&](){
int Sum = Grade_one + Grade_two;
return Sum / 2.0;
};
Grade_one = 42;
Grade_two = 12;
if (Grade_one == Grade_two){
cout<<"Your Grades are Same."<< endl;
}
if(Grade_one >= 50 && Grade_two >= 50 && Grade_one <= 74 && Grade_two <= 74){
cout<<"Hey! You should focus on your study, your grade is concerningly LOW."<< endl;
}
else if(Grade_one <= 49 && Grade_two <= 49){
cout<<"DUDE! you will fail for sure if you don't study."<< endl;
}
else {
cout<<average() <<endl;
// ^^ call the lambda
}
return 0;
}

Answer 4

You need to modify your code slightly. Save this piece of universally useful code somewhere (preferably in a header file):
template <class Lam>
class Expr
{
public:
using ResultType = std::remove_reference_t<decltype((std::declval<Lam>())())>;
operator ResultType() { return lam(); }
ResultType value() { return lam(); }
Expr(Lam&& lam) : lam(std::move(lam)) {}
private:
Lam lam;
};
#define EXPR(...) Expr([&](){return (__VA_ARGS__) ;})
When you #include this piece in your program, you can proceed with minimal modifications:
int Grade_one, Grade_two;
auto Average = EXPR(Grade_one+Grade_two); // note the auto
auto average = EXPR(Average/2.0); // and the decimal point
I however strongly recommend exploring the other answers first.