CODEWITHSUNDEEP
c++if-statementboolean-expressionlogical-or
Verloxide
Verloxide

Reputation: 13

C++ Can't figure out why its giving false positive (newbie)

Hey so I recently started learning C++ and I can't figure out why this problem is giving a false positive all the time.

Maybe someone can help?

// [Included stuff]

using namespace std;

int main() {

    int erg = 5;
    int inp;

    cout << "Answer: 3 + 2: "; 
    cin >> inp;

    if (inp == erg) {
        cout << "True!";
    };

    if (inp <= erg || inp >= erg) {
        cout << "False!";
    }
    else {

    };
}

Image of the Executed Code

Upvotes: 1

Views: 332

Answers (3)

rob
rob

Reputation: 11

if (inp <= erg || inp >= erg) means less than or equal to or greater than or equal to so in effect it always evaluates to true. Use only < (less than) and/or > greater than or use not equal ( != ) instead so code would be if (inp < erg || inp > erg) or even simpler if (inp != erg )

Upvotes: 1

Vlad from Moscow
Vlad from Moscow

Reputation: 310980

The condition in this if statement

if (inp <= erg || inp >= erg) {
    cout << "False!";
}

means that inp can be equal to any number. That is the condition is always evaluates to true so the enclosed statement

    cout << "False!";

is outputted.

It seems you mean either

if (inp != erg) {
    cout << "False!";
}

or (that is only confusing because too complicated)

if (inp < erg || inp > erg) {
    cout << "False!";
}

Or you could write something like

if (inp == erg) {
    cout << "True!\n";
}
else if ( inp < erg ) {
    cout << "False! Less than the result\n";
}
else {
    cout << "False! Greater than the result\n";
}

If you have a condition like this

inp == erg

then its negation will look like

!( inp == erg )

or more readable

not ( inp == erg )

that is the same as

inp != erg

It would be enough to write

if (inp == erg) {
    cout << "True!\n";
}
else {
    cout << "False!\n";
}

Pay attention to that semicolons after closing braces are redundant.

Upvotes: 1

UweJ
UweJ

Reputation: 489

The term 

if (inp <= erg || inp >= erg) {
   cout << "False!";
}

is always true. The term inp <= erg is true for each value of inp in range of [-infinite,erg]. The term inp >= erg is true for each value of inp in range of [erg,infinite]. So the tem inp <= erg || inp >= erg is true for each value of inp in range of [-infinite,infinite].

Wish you much fun coding in C++.

Upvotes: 0

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