Checking if a variable is assigned to another one

[rjp52193]

Alright, so I'm wondering how I can check whether one variable is ASSIGNED to another variable (as in, statement is true if Var A is assigned to var B). However, I cannot simply say if(varA==varB) because in my program, varA could also be equal to varC, which has an if statement as well and would ruin everything. Any help?

[Framework]

What you're asking is quite strange, because it doesn't make much sense. Can you refine your question more?

_Wazzak

[clanmjc]

What are are you comparing, the values, the addresses? Please clarify, post some code.

[Disch]

variables do not hold assignment information. They only hold a value.

int A = 5;
int B = 6;


B = A;  // here, A's value gets stored in B

// since A was 5, this means that now B is 5
// at this point, the only thing B knows is that it contains 5.  It does not
//  know that the 5 came from A.  There is no way to check whether or not
//  A was assigned to B or vice versa. 

If you want a variable that contains another variable (and not just a value), then maybe you want a pointer... but as Framework said this is very strange:

int A = 5;
int* B = nullptr;  // B points to nothing
int C = 5;

// make B point to A
B = &A;

// now B == &A, so you can use that to check whether or not that
//   assignment occurred:

if(B == &A)
{
  // will execute
}

if(B == &C)
{
  // will not execute, even though A==C
}

[rjp52193]

Thanks guys I'll try to post a simplified version of what I'm doing.

char x;
float varA=0, varB=0, varC, amount;

cout<<"Enter a or b:";
cin>>x;

if(x=='a')
varC=varA;

else if(x=='b')
varC=varB;

cout<<"Enter the amount to add or subtract:";
cin>>amount;

*** if(varC==varA)
varC+=amount;

***else if(varC==varB)
varC-=amount;

The lines marked with asterisks are where I'm having a problem, because both statements will be true since both A and B are set to zero initially. (The first "if" is used, the "else if" gets overridden.)

Also, the value of x gets changed in other spots of my program so I can't use if(x=='a') etc. again. And I have to have both values set to zero initially. So any help?

[clanmjc]

Well a quick simple solution would be...

instead of if(varC==varA) do if(x=='a') and the else if (x=='b') and proceed as you've done.

You already have x which appears to be your "condition", reuse it.

Also, I know this is a small program, but I'd suggest using meaningful names for all variables whenever you can, if not for anything other than making it habit.

[vlad from moscow]

Introduce a logical variable and do not bother:)

bool AsA = false;

if(x=='a') varC=varA, AsA = true;

else if(x=='b') varC=varB;

if ( AsA ) varC+=amount;
else varC-=amount;

[rjp52193]

My value of x gets changed in other parts of the code that I didn't include, so is there any other alternative?

[clanmjc]

Yes, use a flag as vlad has suggested.

[rjp52193]

Oh I get it, thanks for your help!

[Disch]

Err.... I wouldn't use a flag. I would use a pointer. Going to pitch this at you again:

char x;
float varA=0, varB=0, amount;
float* varToUse = nullptr;

cout<<"Enter a or b:";
cin>>x;

if(x=='a')
  varToUse = &varA;
else if(x == 'b')
  varToUse = &varB;
else
  /* give some kind of error to the user and abort */


cout<<"Enter the amount to add or subtract:";
cin>>amount;

// no need to do any more 'ifs' here, just use the pointer
*varToUse += amount;  // this will modify varA or varB depending on which
   // one it points to. 

[clanmjc]

@Disch - I was going to suggest something similiar except for how if a or b += or -=.

[Disch]

Ah I missed that bit. Okay that make sense.