Sorry for Dumb question but im stumped

[gfitzp]

Hey this is my first post. Im trying to teach myself c++ and have reached the Arrays section in the documentation of this site.
However, I cant figure out how the example of the 2 dimensional array works. I can see how the table works mathmatically but I cant see the process of filling each slot in the array. Surely as 'n' increases so does 'm' and therefore only [0][0],[1][1],[2][2],[3][3],[4][4] and [5][5] get filled? Im really rusty at maths etc so hopefully some of you could help clear this up for me? The code im refering to is below. And heres a link to the page:
http://www.cplusplus.com/doc/tutorial/arrays/

I appreciate your help.

Cheers, Gareth.

#define WIDTH 5
#define HEIGHT 3

int jimmy [HEIGHT][WIDTH];
int n,m;

int main ()
{
for (n=0;n<HEIGHT;n++)
for (m=0;m<WIDTH;m++)
{
jimmy[n][m]=(n+1)*(m+1);
}
return 0;
}

[KezRst]

Here's a play-by-play of what happens in this program:

for a moment lets pretend we just have this:

int main() {
  for ( n=0; n<HEIGHT; n++ ) {
    jimmy[n] = n+1;
  }
  return 0;
}

As it loops, it will do

jimmy[0] = 1;
jimmy[1] = 2;
jimmy[2] = 3;

That's how it will iterate with a single dimentional loop. Now we can add in a nested loop:

int main() {
  for ( n=0; n<HEIGHT; n++ ) {
    
    for (m=0;m<WIDTH;m++)
      jimmy[n][m]=(n+1)*(m+1);

  }
  return 0;
}

jimmy[0][0] = 1;

///n, AKA HEIGHT is still 0, because we're doing the nested loop still, not the first loop.
jimmy[0][1] = 2;
jimmy[0][2]
//etc
jimmy[1][0]
jimmy[1][1]
//etc, until
jimmy[3][5]


So you can see, the inner loop will run it's course entirely before the outer loop cycles again. That is why every dimension of your variable jimmy is being set.

[gfitzp]

Thats great mate thanks for that. I suspected something like that but didnt know how it worked.

Cheers gareth