C++ if-else if Issues [closed] - c++

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I'm having issues with my program below. It should convert numbers between 1-100 to AA,BA,BB,CB,CC,D,F. But it stops working and shows "BA" if I enter number less than 84. I checked the code. But I don't understand what is the problem.
#include <iostream>
using namespace std;
int main() {
int secenek,notu;
cout << "Not Dönüştürücü" << endl;
cout<<"Başlamak için 1'e basın:\n";
cin>>secenek;
if (secenek==1)
{
cout<<"Dönüştürülecek not: ";
cin>>notu;
}
if (notu<0 || notu>100)
{
cout<<"Geçerli bir not girin.\n";
}
else if (notu>=90)
{
cout<<"AA";
}
else if (notu<90 || notu>84)
{
cout<<"BA";
}
else if (notu<85 || notu>79)
{
cout<<"BB";
}
else if (notu<80 || notu>74)
{
cout<<"CB";
}
else if (notu<75 || notu>69)
{
cout<<"CC";
}
else if (notu<70 || notu>59)
{
cout<<"D";
}
else if (notu<60)
{
cout<<"F";
}
}

Answer 1

you made a logical error:
else if (notu<90 || notu>84)
should be
else if (notu<90 && notu>84)
and the same goes for all the following conditions.
EDIT as #Jarod42 suggested; you don't even need to check notu<90 anymore... your code could look like this:
if (notu<0 || notu>100)
{
cout<<"Geçerli bir not girin.\n";
}
else if (notu>=90)
{
cout<<"AA";
}
else if (notu>84)
{
cout<<"BA";
}
else if (notu>79)
{
cout<<"BB";
}
etc...

Answer 2

Your condition
else if (notu<90 || notu>84)
will always be true, whatever notu is set to. You probably mean
else if (notu < 90 && notu > 84)

Answer 3

The problematic part:
else if (notu<90 || notu>84)
{
cout<<"BA";
}
else if (notu<85 || notu>79)
{
cout<<"BB";
}
else if (notu<80 || notu>74)
{
cout<<"CB";
}
else if (notu<90 || notu> 84) will trigger on any notu lower than 90 and on any notu higher than 84. That's all pretty much all who survived the earlier check.
Correct implementation would be else if (notu<90 && notu> 84) which will only trigger if both conditions are met.
My C++ is a bit rusty, but if I remember correctly one could even write else if (84 < notu < 90).
EDIT: else if (84 < notu < 90) isn't valid C++ syntax.

Answer 4

The main problem is that you're using || where && would be logically correct.
But you don't really need && either - you can simplify a bit since in the else branch you already know that the corresponding if condition is false.
Like this:
if (notu < 0 || notu > 100)
{
cout << "Geçerli bir not girin.\n";
}
else if (notu >= 90)
{
cout << "AA";
}
else if (notu >= 85) // Already know that it's < 90, because it's not >= 90
{
cout << "BA";
}
// ...
// ...
else if (notu >= 60) // Already know that it's < 70
{
cout << "D";
}
else // Already know that it's < 60
{
cout << "F";
}