if statement does not work with || (or)

Question

i'm new at c++ i was trying to write a program and i found a problem with it even after i used a simpler program (bellow) i couldn't figure it out

when i input numbers such as 85 or 55, even though program shouldn't respond, it does

#include "stdafx.h"
#include <iostream>
#include <cmath>

using namespace std;

int main()
{
    int a=0;
    cin >> a;
    if(a<25 || 30<a<50 || 60<a<75)
    {
        cout << "see it does't work\n";
    }
    return 0;
}

please help me

Answer 1

#include "stdafx.h"
#include <iostream>
#include <cmath>

using namespace std;

int main()
{
    int a=0;
    cin >> a;
    if(a<25 || (30<a && a<50) || (60<a && a<75))
    {
        cout << "see it does't work\n";
    }
    return 0;
}

Answer 2

Your condition should be this :

if(a<25 || (30<a && a<50) || (60<a && a<75))
{
    cout << "see it does't work\n";
}

Answer 3

Your if statement is malformed.

Each expression must evaluate to a true or false, and you cannot do things like upper/lower bounding.

Try this:

int main()
{
    int a=0;
    cin >> a;
    if(a<25 || (a > 30 && a < 50)  || (a> 60 && a <75))
    {
        cout << "see it does't work\n";
    }
    return 0;
}

Answer 4

Try

#include "stdafx.h"
#include <iostream>
#include <cmath>
using namespace std;

int main()
{
    int a=0;
    cin >> a;
    if ((a<25) || ((30<a) && (a<50)) || ((60<a) && (a<75)))
    {
        cout << "see it does't work\n";
    }
    return 0;
}

Parenthesis are your friend. Each binary conditional expression will have a left part (a), operator (<) and right part (25). You have to break everything down to be expressed in this way.

Answer 5

what is happening in the below if statement is:

if(a<25 || 30<a<50 || 60<a<75)

when a = 85, 30 is always less than a, and hence true (which means 1 in c++ when converted to integer) and then 1 is always less than 50, hence true.

So, consider changing your if statement to

if ( a < 25 || (30 < a && a < 50) || ( 60 < a && a < 75) )

Answer 6

Theres no x < z < y kind of statement in C++. You should separate those statements into binary parts: x < z && z < y .

Let me rewrite that for you:

#include <iostream>

int main() {
    int a = 0;
    std::cin >> a;
    if(a < 25 || (30 < a && a < 50) || (60 < a && a < 75)) {
        std::cout << "See? It does work!\n";
    }
    return 0;
}