changing numbers in an array

[Zachary]

(that's not the best title...sorry about that!)

I have an array with the numbers 1,2,3,2. I want to swap each integer with its mod12 complement (1 swaps with 11, 2 swaps with 10, 3 swaps with 9), to create a list of 16 possibilities:

1 2 3 2
1 2 3 10
1 2 9 2
1 2 9 10
1 10 3 2
1 10 3 10
1 10 9 2
1 10 9 10
11 2 3 2
11 2 3 10
11 2 9 2
11 2 9 10
11 10 3 2
11 10 3 10
11 10 9 2
11 10 9 10

See the pattern? Keep the first three numbers the same, and swap the last one. Then keep the first two numbers the same, swap the third one, and then the last one...etc...

The code I have written only displays the last one, 11 10 9 10.

[code=c++]
#include <iostream>

using namespace std;

int main()
{
int i, j, k, l;
int array[4] = {1,2,3,2};

for (i=0; i<2; i++)
{
if (i = 0)
{
array[0] = array[0];
}
if (i = 1)
{
array[0] = 12-array[0];
}
for (j=0; j<2; j++)
{
if (j = 0)
{
array[1] = array[1];
}
if (j = 1)
{
array[1] = 12-array[1];
}
for (k=0; k<2; k++)
{
if (k = 0)
{
array[2] = array[2];
}
if (k = 1)
{
array[2] = 12-array[2];
}
for (l=0; l<2; l++)
{
if (l = 0)
{
cout << array[0] << " " << array[1] << " " << array[2] << " " << array[3] << endl;
}
if (l = 1)
{
cout << array[0] << " " << array[1] << " " << array[2] << " " << 12-array[3] << endl;
}
}
}
}
}
return(0);
}
[/code]

I'm sure there's something elementary that I'm missing.
Two part question:
1) Can you help alter my existing code so that it prints out all 16 possibilities?
2) Can you suggest a better way of going about this process?

[jsmith]

First, walk the array and change every value to 12 - x.
Then, sort the array in increasing order.
Then, use std::next_permutation().

Oops, misread original problem. Never mind. Recalculating...

[jsmith]

Every one of your if() statements is an assignment, not a comparison.

[Zachary]

I think the sorting might defeat the purpose of what I need to do. I need to work from 1 2 3 2, as opposed to 1 2 2 3. (Did I misunderstand what you were suggesting?)

Thanks!

[Zachary]

Oh! That's it exactly! Thanks, jsmith. I can't believe I made such a boneheaded mistake.

Thanks a lot -- I'll proofread better next time... :-)

[jsmith]

Ok.

I wrote the entire program in 14 lines, include 2 blank lines, 1 #include, and 1 to declare the array. :)

[Zachary]

Oooh! That's exciting -- care to share? :-)

(If you think I could understand the code, that is!)

[jsmith]

Hmm, ok, since your code works with the == instead of =.

#include <iostream>

template< typename T, int N >
int ArraySize( T (&)[ N ] )
{ return N; }

int main() {
   int a[] = { 1, 2, 3, 2 };
   for( int i = 0; i < ( 1 << ArraySize( a ) ); ++i ) {
       for( int j = 0; j < ArraySize( a ); ++j )
           std::cout << ( i & ( 1 << ( ArraySize( a ) - j - 1 ) ) ? 12 - a[ j ] : a[ j ] ) << ' ';
       std::cout << std::endl;
   }
}

EDIT: this code works for any array size from 1 to 31 inclusive. All you have to do is add or remove elements from the array; the rest of the code is unchanged. I could have added a BOOST_STATIC_ASSERT to guarantee the array size isn't too big, but that would've been 2 more lines of code.

[Zachary]

I think I understand most of this (my brain is still digesting...). But I don't understand what line 3 is. I haven't done anything with templates before...

[Bazzy]

A template is used for a function or a class so it can be more generic

in that case T could be any type and the argument of ArraySize be an array of type T with any size ( N )

http://www.cplusplus.com/doc/tutorial/templates.html