Alterations with a integer in c++

Question

This is easy for you. I am busy with a test using c++. I have 2 values:

0 and 1

I can find random number between. Now i want to alternate between them. If i get "1" in step one then in step two I want to get "0" and in step three "1" again where it alternate

step1 = 1
step2 = 0
step3 = 1
step4 = 0

I tried increment and decrements

  int value;
  if(value == 0)
  {   
      value = value + 1;
  }
  else if(value == 1)
  {
      value = value -1;
  }

This code does not work. If it sees a 0 it will become 1 but the next step the value will be 1 again.

You mean that there are series of steps, and in first step if you get 1, then in next step you get zero, and then 1 again, and so on? — SandBag_1996, Aug 23 '12 at 17:33
@jrok Depends on the compiler, some will initialize to zero. — grieve, Aug 23 '12 at 17:41
@grieve, it is officially undefined. Some compilers *do* define the behavior, but it's generally not a good idea to rely on that. It caused a security vulnerability in OpenSLL not too long ago (see also http://blog.llvm.org/2011/05/what-every-c-programmer-should-know.html , http://blog.llvm.org/2011/05/what-every-c-programmer-should-know_14.html , http://blog.llvm.org/2011/05/what-every-c-programmer-should-know_21.html , https://www.securecoding.cert.org/confluence/display/seccode/EXP33-C.+Do+not+reference+uninitialized+memory ) — Max Lybbert, Aug 23 '12 at 17:44
@MaxLybbert Agreed that you should not rely on it, just pointing out that it may be initialized to zero depending on the compiler you are using. — grieve, Aug 23 '12 at 18:01

grieve · Accepted Answer · 2012-08-23T17:58:42.433

3

If you really only ever need 0 and 1:

unsigned int value = 0;

while (1) {
   value = (value + 1) & 1;
   // do whatever is needed with value;
}

This works because in binary 0 + 1 = 1, and 1 + 1 = 10. The '& 1' portion tells us to always take the last bit.

edited Aug 23 '12 at 17:58

answered Aug 23 '12 at 17:39

grieve

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@David uint is short hand for unsigned int. It was not a typo of unit. :) – grieve Aug 23 '12 at 17:45
C++ defines no such type as uint. Must be unsigned int? – SandBag_1996 Aug 23 '12 at 17:46
@grieve sorry, I made a typo. I meant what was `uint` not `unit`. lol – David G Aug 23 '12 at 17:48
1

@UnderDog Fixed. In my C++ code we had defined it, and I just got lazy in using it here. – grieve Aug 23 '12 at 17:59

score 1 · Answer 2 · edited May 23 '17 at 12:27

1

Wild guess: You are using floating point types (doubleor float) to represent those numbers. You can't compare those types using the == operator, you need to take their precision into account.

Take a look at this question on how to compare floating point types.

edited May 23 '17 at 12:27

Community

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answered Aug 23 '12 at 17:33

Marcus Riemer

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No i am not using floats or doubles – Johan Dela Aug 23 '12 at 17:35
1

So by saying "I can find random number between 0 and 1" you mean "randomly 0 or 1"? – Marcus Riemer Aug 23 '12 at 17:37
That i can do with rand()%2, i'm trying to alternate between 0 and 1. Like if i get 1 in a step then in the next step i get 0 and next step 1 again – Johan Dela Aug 23 '12 at 17:39
1

I was only trying to say, that e.g. 0.5 is also "between 0 and 1". Thats what initially confused me ;) – Marcus Riemer Aug 23 '12 at 17:41

score 1 · Answer 3 · answered Aug 23 '12 at 17:36

1

put in a bool switch with your if statements, eg

bool firstHit = false;
if(value == 0 && firstHit == false)
{   
  value = value + 1;
  firstHit = true;
}
else if(value == 1 &&firstHit == true)
{
  value = value -1;
  firstHit = false;
}

answered Aug 23 '12 at 17:36

Him_Jalpert

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1

How exactly is an extra, redundant, variable going to help? – Mike Seymour Aug 23 '12 at 17:50
2

I think you're missing the fact that the second part is **else** if. The intent would become more clear if it was just if. – chris Aug 23 '12 at 17:51

score 1 · Answer 4 · answered Aug 23 '12 at 17:40

1

Your code is fine dude. I tested it, and its working.

#include <iostream>

using namespace std;

int main ()
{

    int value=1; //Say first step

  for (int i=0 ; i <= 10; i++ )
{
    if(value==0)
    {
        value=value+1;
    }
    else if (value==1)
    {
        value=value-1;
    }
         cout << "Step "<<i<<": "<<value<<"\n";
}

  return 0;
}

answered Aug 23 '12 at 17:40

SandBag_1996

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@JohanDela, And what *is* your compiler? Note that this `value` is initialized, too. – chris Aug 23 '12 at 17:48

score 1 · Answer 5 · answered Aug 23 '12 at 17:45

The code you're showing doesn't initialize value to anything.

Other than that,

if(value == 0)
  {   
      value = value + 1;
  }
  else if(value == 1)
  {
      value = value -1;
  }

This looks like it should work fine if you just want to alternate between 1 & 0, as it will switch it every time you iterate through it.

score 0 · Answer 6 · answered Aug 23 '12 at 19:29

0

Simplest :

value = 1 - value;

There's a <g> before the colon, but the system software seems to not want to display it.

answered Aug 23 '12 at 19:29

Pete Becker

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Alterations with a integer in c++

6 Answers6