compacting similar nested for loops

[SplaTTer]

I have a piece of code consisting of k nested for loops, for example:

int k = 5;
int *p = new int[k];
double x,y; //x is read from file


for(p[0]=0;p[0]<=6;p[0]++)
for(p[1]=0;p[1]<=3;p[1]++)
for(p[2]=0;p[2]<=3;p[2]++)
for(p[3]=0;p[3]<=3;p[3]++)
for(p[4]=0;p[4]<=3;p[4]++)
y = assign(x, p);

This works, however, in a more general version k can be anywhere from
1 to 10. Therefore p will be of array size k and range from p[0] to
p[k-1], and I will only need k number of nested for loops. I could
write code for all the different possible conditions and use if
statements to select the proper one, but i would rather see if there
is a way to do it in a more compact manner (like with a recursive
function or even using the goto statement).

 

[Victor Bazarov]

I have a piece of code consisting of k nested for loops, for example:

int k = 5;
int *p = new int[k];
double x,y; //x is read from file


for(p[0]=0;p[0]<=6;p[0]++)
for(p[1]=0;p[1]<=3;p[1]++)
for(p[2]=0;p[2]<=3;p[2]++)
for(p[3]=0;p[3]<=3;p[3]++)
for(p[4]=0;p[4]<=3;p[4]++)
y = assign(x, p);

This works, however, in a more general version k can be anywhere from
1 to 10. Therefore p will be of array size k and range from p[0] to
p[k-1], and I will only need k number of nested for loops. I could
write code for all the different possible conditions and use if
statements to select the proper one, but i would rather see if there
is a way to do it in a more compact manner (like with a recursive
function or even using the goto statement).

Yes, recursion should work. And I've read it many times that any
recursion can be emulated with an array.

void nestedLoop(int p[], int upperlimit[],
unsigned level, unsigned maxlevel,
double& x, double &y)
{
if (level < maxlevel)
for (p[level] = 0; p[level] < upperlimit[level]; ++p[level])
nestedLoop(p, upperlimit, level+1, maxlevel, x, y);
else
y = assign(x, p);
}

....
int upperlimit[] = { 6,3,3,3,3 }; // not sure of the significance
// of the first one's being 6.
nestedLoop(p, upperlimit, 0, k, x, y);

(Is this right? I didn't test it)

Victor

 

[SplaTTer]

Thanks a bunch Victor. That worked great. There was only a small
problem with the for loops going to one less than each of the
upperlimits, but that was easily fixed.

To answer your question about the significance of the first element in
the upperlimit array = {6,3,3,3,3}: the first loop is the most
important in my program, and 6 happens to be closer to +infinity than
3. So in other words it was just specific to what i'm using the
assign(x,p) function for.

Thanks,

-Kent