Using an Array as a Whille loop condition

1
votes

I am trying specify a condition by saying that if an array is not equal to an array run loop. So for example:

array1 [1,2,3]

array2 [1,2,3]

Here array1 does equal array2 as the elements in 0 in both arrays are the same, the elements in 1 in both arrays are the same and so on...

The code I have so far doesn't seem to work. Is there a way of comparing two arrays and if all elements in one match all the elements in the second one the condition is true.

Here is my test code:

int C1Mean[3];
int C2Mean[3];
int prv_mean1[3];
int prv_mean2[3];

while (C1Mean[3] = prv_mean1[3] && C2Mean[3] = prv_mean2[3])
{
    //code
}

Thanks chaps.

6
c++arrayswhile-loop
You access your arrays out of bounds, and you are using assignments (single =) instead or comparisons. Try something like while (C1Mean[2] == prv_mean1[2] && C2Mean[2] == prv_mean2[2] ...) – quantdev
Well, the most basic way would be to compare every element of the first array with each element of the second. Next, don't invoke undefined behavior by accessing memory beyond your arrays... – Ed S.

6 Answers

4
votes

As commented you access your arrays out of bounds, and you are using assignments (single =) instead or comparisons (==).

To compare your arrays (element by element), you can use std::equal :

while(std::equal(std::begin(C1Mean), std::end(C1Mean), std::begin(prv_mean1))
   && std::equal(std::begin(C2Mean), std::end(C2Mean), std::begin(prv_mean2)))
{
 ...
}

Or without c++11 :

while(std::equal(C1Mean, C1Mean + sizeof C1Mean / sizeof *C1Mean, prv_mean1)
   && std::equal(C2Mean, C2Mean + sizeof C2Mean / sizeof *C2Mean, prv_mean2))
{
 ...
}
2
votes

In c++11, you may use std::array, and use ==:

std::array<int, 3> C1Mean;
std::array<int, 3> C2Mean;
std::array<int, 3> prv_mean1;
std::array<int, 3> prv_mean2;

while (C1Mean == prv_mean1 && C2Mean == prv_mean2)
{
    //code
}
1
votes

You are not using comparison operator (==) but assignment (=), so you change the value of CMean[i] in the condition and the condition would be false only when one of prv_mean2 would be equal to zero. And no, you can't compare the whole arrays.

0
votes

If you are able to use c++11 you can use a generic function. The generic function is:

bool equal(beginIterator, endIterator, beginIterator Other);

This generic function will compare all values in a range. Note that the second array must be at least as long as the first array.

Since an array is nog an object you cannot use arr.begin () and you should use std::begin(arr) and std::end(arr). These functions come with #include.

Furthermore, if you can use c++11 you can also use the standad container std::array or std::vector. Then you can just state arr1 == arr2.

Note: I wrote this on my mobile and didn't check whether the generic function actually works on arrays. I will check this when at home again and eventually remove my post.

0
votes

You can create a function to compare the two arrays that will return 1 if they are equal and 0 otherwise. Say, for example, 

while(areEqual(C1Mean,prv_mean1) && areEqual(C2Mean,prv_mean2))
{
 //Perform your task
}

where 

int areEqual(int array1[],int array2[])
{
 //compare them and return 1 if equal else return 0;
}
-2
votes

It seems like you need a double equals("=="). Try: 

while (C1Mean[3] == prv_mean1[3] && C2Mean[3] == prv_mean2[3])
{
    //code
}