Double negation in c++ using if

Question

Problem:

I am practicing from my college's introduction problem set of creating a program where the user introduces four variables a, b, c, d and: if a is in (c; d) AND b isn't in (c; d) the program should print a, b and a+b; otherwise it should print a, b and a-b:

I noticed that if the user introduces a, b such that BOTH statements are false it prints a+b instead of a-b. Why does it happen?

Attempt:

#include<iostream>
using namespace std;

int main()
    {int a,b,c,d;
    cout<<"Introduza a: ";
    cin>>a;
    cout<<"Introduzca  b: ";
    cin>>b;
    cout<<"Introduzca c: ";
    cin>>c;
    cout<<"Introduzca d: ";
    cin>>d;
    if( (c<a<d) && ((b<c || d<b)))
        {cout<<"a= " <<a <<"\n";
        cout<<"b= " <<b << "\n";
        cout<<"a+b= " <<a+b <<"\n";
        }
    else
        {cout<<"a=" <<a <<"\n";
        cout<<"b= " <<b <<"\n";
        cout<<"a-b= " <<a-b <<"\n";}
        }

Comparison operators, e.g. `'<'` have operator precedence 9 and *left-to-right* associativity. See [C++ Operator Precedence](https://en.cppreference.com/w/cpp/language/operator_precedence) — David C. Rankin, Mar 17 '19 at 00:16
Consider adopting a standard and more readable formatting style. — Retired Ninja, Mar 17 '19 at 00:18
[Math-like chaining of the comparison operator - as in, "if (5 val2 > val3) a valid comparison in C?](https://stackoverflow.com/q/38643022/995714), [Language support for chained comparison operators (x < y < z)](https://stackoverflow.com/q/4090845/995714) — phuclv, Mar 17 '19 at 00:26
@RetiredNinja Apart from that one would not indent the braces, it's Horstmann style... — Aconcagua, Mar 17 '19 at 00:57
@Aconcagua The lack of whitespace after the opening brace is the worst though. — Retired Ninja, Mar 17 '19 at 05:20

score 2 · Answer 1 · 2019-03-17T02:09:36.263

2

in programming languages like C++, C, Java, PHP, .. something like (c<a<d) is spread out to (c < a && a < d). The second thing is that you do not need double parenthesizes here ((b<c || d<b)). This entire line:

if( (c<a<d) && ((b<c || d<b)))

should look like:

if (c < a && a < d && (b < c || d < b))

Hope this helps!!!!

CLARIFICATION PER COMMENT: What I mean in mathematics you write a < b < c in programming language you write this as a < b && b < c. In programming a < b < c is the same as (a < b) < c which in turns mean if a is less than b it will return 1 thus producing 1 < c. If a is greater or equal to b a < b will return 0 thus producing 0 < c.

edited Mar 17 '19 at 02:09

answered Mar 17 '19 at 00:12

6

You should say "In C++", not "In programming". There are programming languages where `c < a < d` actually means `c < a && a < d`. – Keith Thompson Mar 17 '19 at 00:18
"_in programming languages like C++, C, Java, PHP, .. something like `(c – Algirdas Preidžius Mar 17 '19 at 01:43
@AlgirdasPreidžius what do you mean? – Mar 17 '19 at 01:49
@Gox In the quote, that I quoted, you state, that "_something like `(c – Algirdas Preidžius Mar 17 '19 at 01:59
@AlgirdasPreidžius I updated my answer. – Mar 17 '19 at 02:10

Double negation in c++ using if

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1 Answers1