How to get a both numbers are equal or this one is greater?

Question

In c++ I have am going through a online course and I have no idea where else to find the answer to this or good c++ websites to learn from. The code below is supposed to give the output: Both numbers are equal OR Greater value is a/b.

#include <iostream>    
#include <string>    
using namespace std;    
int main(int argc, char* argv[])    
{    
  int a,b,c=0;    
  cout<<"Enter value of 1st variable: ";    
  cin>>a;    
  cout<<"Enter value of 2nd variable: ";    
  cin>>b;    

  {
    if ( !(a == b));
    !true;

    cout << "Both are equal";
  }
  !false;

  {
    if (a>b)
      c = a; 
    if (b>a);
      c = b; 
    cout << "Greater value is " << c;
  }
}

I don't know any other ways to give the output I want.

So if the first input is 50 and the second is 50 I get the output Both are equalGreater value is 50

If the first is 50 and the second is 49 I get the output Both are equalGreater value is 49.
If the first is 50 and the second is 90 I get the output Both are equalGreater value is 90.

_`!true;`_ is a NOP. You go back to the basic chapters of your c++ textbook please! — πάντα ῥεῖ, Apr 06 '15 at 18:59
The website I am using hasn't covered NOPs I used it after I stumbled upon it during research. — print'Words', Apr 06 '15 at 19:10
@drescherjm I want the first to set c to b if it's bigger (I had a mistake in the question, edited it now.) The 2nd is to categorize it so that if a is the b is true cout Both are equal — print'Words', Apr 06 '15 at 19:13
Remove the semicolons on both of these if () statements. And do as @πάνταῥεῖ suggested go back to the basic chapters of your c++ textbook. — drescherjm, Apr 06 '15 at 19:15
***The website I am using hasn't covered NOPs*** I do not believe that one can learn c++ from a website. Get a book. — drescherjm, Apr 06 '15 at 19:17
Yes. The semicolon ends the if statement. So the next line executes regardless of the condition. — drescherjm, Apr 06 '15 at 19:18
`!true;` does not do anything is what a NOP is. Same with `!false;` — drescherjm, Apr 06 '15 at 19:20
learn c/c++ snytax for if statements. This is not LISP, or whatever syntax you got that from. — MikeMB, Apr 06 '15 at 19:27
@MikeMB i'm not getting syntax errors I am getting the wrong output I want. — print'Words', Apr 06 '15 at 19:28
Because you used a syntax does not mean what you think it means. Just because the syntax of your program is valid, it doen't mean it is the correct one for what you want to express. — MikeMB, Apr 06 '15 at 19:34
I recommend that you take a look at this question for book recommendations: http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list — drescherjm, Apr 06 '15 at 20:31

score 1 · Answer 1 · answered Apr 06 '15 at 19:39

You have several problems with basic C++ syntax.

An if statement should not normally end with a semicolon:

if ( !(a == b));

Should be:

if ( !(a == b))
//            /\ No semicolon here!

The braces for an if statement should go after the closing parenthesis. This:

{
if (!(a == b))
}

Should be:

if (!(a == b))
{
}

Neither of these lines do anything:

!true;
!false;

Extra braces are allowed, which is why your compiler is not complaining about them. Just because I can do this, doesn't mean I should:

int main()
{
  {
    {
      {
        // code here
      }
    }
  }
}

MikeMB · Accepted Answer · 2015-04-06T20:37:56.753

Apparently you don't know how to use if else correctly in c++. You can look them up e.g. here.

One correct way your program could look like:

#include <iostream>    
#include <string>    
using namespace std;
int main(int argc, char* argv[])
{
    int a, b, c = 0;
    cout << "Enter value of 1st variable: ";
    cin >> a;
    cout << "Enter value of 2nd variable: ";
    cin >> b;


    if (a == b){
        cout << "Both are equal";
    } else {
        if (a > b) {
            c = a;
        } else if (a < b){ //<-- As indicated by @Thomas Matthews you don't actually need the third check here
            c = b;
        }
        cout << "Greater value is " << c;
    }
}

Other ways to write this:

if (a == b){
    cout << "Both are equal";
}else if (a > b) {
    cout << "Greater value is " << a;
} else {        
    cout << "Greater value is " << b;
}

OR (less obvious):

int t = a - b;
switch ((t > 0) - (t < 0)){ //<-- effectively computing the sign of t
    case -1: cout << "Greater value is " << b; break;
    case 0: cout << "Both are equal"; break;
    case 1: cout << "Greater value is " << a; break;
}

I wasn't aware python and c++ were so similar with if statements, do you know any more efficient way of doing this? — print'Words', Apr 06 '15 at 19:39
@print'Words': In terms of run time efficency or fewer lines of code? There are a few alternate ways how to wirte it, but I doubt any of them has any significant impact on the performance. — MikeMB, Apr 06 '15 at 20:05
@print'Words': come to think of it: You can do it with fewer lines of code (see edit), but not really with less code . — MikeMB, Apr 06 '15 at 20:23

score 0 · Answer 3 · answered Apr 06 '15 at 20:02

0

Here is a simple fragment:

if (a == b)
{
  cout << "a == b";
}
else
{
  if (a < b)
  {
    cout << "a < b";
  }
  else
  {
    cout << "a >= b";
  }
}
cout << "\n";

You only need 2 comparisons.

answered Apr 06 '15 at 20:02

Thomas Matthews

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How to get a both numbers are equal or this one is greater?

3 Answers3