scm@cs.ed.ac.uk (Santa C Maria) (06/20/91)
This is probably a rather silly question. I would be glad, if you
can give me a hint. I want to implement a number of loops in this
manner:
for ( i[0] = 0; i[0] < x[0]; ++i[0] ) {
for ( i[1] = 0; i[1] < x[1]; ++i[1] ) {
......
......
for ( i[m-1] = 0; i[m-1] < x[m-1]; ++i[m-1] ) {
do_something_here();
}
......
}
}
do_something_here() is thus executed x[0]*[x[1]* ... *x[m-1] times.
The problem is that m, x[0], ... x[m-1] all depend upon run-time
values. The question is how do I code this?
Thanks in advance for your help.pckim@unisql.UUCP (Pyung-Chul Kim) (06/21/91)
In article <12844@skye.cs.ed.ac.uk>, scm@cs.ed.ac.uk (Santa C Maria) writes: > for ( i[0] = 0; i[0] < x[0]; ++i[0] ) { > for ( i[1] = 0; i[1] < x[1]; ++i[1] ) { > ...... > for ( i[m-1] = 0; i[m-1] < x[m-1]; ++i[m-1] ) { > do_something_here(); > } > ...... > } > } > > The problem is that m, x[0], ... x[m-1] all depend upon run-time > values. The question is how do I code this? > After determine m and allocate array x, and initialize elements of it, and call the following recursive funtion foo(0): /* assume m and x are global variables */ foo(j) int j; { int i; if(j == m-1) for(i = 0; i < x[j]; i++) do_something_here(i,j); else for(i = 0; i < x[j]; i++) foo(j+1); } Hope it helps -- Pyung-Chul Kim UniSQL, Inc. 9390 Research Blvd., Kaleido II, Suite 220, Austin, TX 78759 Internet: execu!sequoia!unisql!pckim@cs.utexas.edu UUCP: {uunet, cs.utexas.edu!execu}!sequoia!unisql!pckim TEL: (512)343-7297 Ext. 332 FAX: (512)343-7383
grue@cs.uq.oz.au (Frobozz) (06/21/91)
In <1377@unisql.UUCP> pckim@unisql.UUCP (Pyung-Chul Kim) writes: ]In article <12844@skye.cs.ed.ac.uk>, scm@cs.ed.ac.uk (Santa C Maria) writes: ]> for ( i[0] = 0; i[0] < x[0]; ++i[0] ) { ]> for ( i[1] = 0; i[1] < x[1]; ++i[1] ) { ]> ...... ]> for ( i[m-1] = 0; i[m-1] < x[m-1]; ++i[m-1] ) { ]> do_something_here(); ]> } ]> ...... ]> } ]> } ]> ]> The problem is that m, x[0], ... x[m-1] all depend upon run-time ]> values. The question is how do I code this? ]> ]/* assume m and x are global variables */ ]foo(j) ]int j; ]{ ] int i; ] if(j == m-1) for(i = 0; i < x[j]; i++) do_something_here(i,j); ] else for(i = 0; i < x[j]; i++) foo(j+1); ]} I think that this can be done without a recursive function. Something like the following code should be able to do what is required. I should also mention that I haven't checked the following code for correctness, so don't blame me when it don't work. i[0] = 0; for(j=0;j>=0;) { if(i[j] == x[j]) { /* terminate a loop */ j--; /* to prev loop */ i[j]++; /* inc this counter */ continue; } if(j != m-1) { /* not at deepest level of looping */ j++; i[j] = 0; continue; } do_something(); i[j]++; } An alternative would be to do something like: for(j=0,n=1;j<m;j++) /* calc number of times through loop */ n *= i[j]; for(j=0;j<n;j++) { for(k=j,j1=m-1;j1>=0;j1--) { i[j1] = k % x[j1]; k /= x[j1]; } do_something(); } which first finds out how many times the loops will execute do_something and then it sets up a loop that big. At the start of every iteration, it recalculates the loop index array i[]. This isn't a very efficient method, but it does avoid the recursion that was present. There should be methods to save recalculating the entire index array --- it should suffice to stop recalculating when one of the elements doesn't change. i.e. Change the line: i[j1] = k % x[j1]; to tmp = k % x[j1]; if(i[j1] == tmp) break; i[j1] = tmp; Again I haven't verified this code either. Pauli seeya Paul Dale | Internet/CSnet: grue@cs.uq.oz.au Dept of Computer Science| Bitnet: grue%cs.uq.oz.au@uunet.uu.net Uni of Qld | JANET: grue%cs.uq.oz.au@uk.ac.ukc Australia, 4072 | EAN: grue@cs.uq.oz | UUCP: uunet!munnari!cs.uq.oz!grue f4e6g4Qh4++ | JUNET: grue@cs.uq.oz.au --
jos@and.nl (J. Horsmeier) (06/21/91)
In article <12844@skye.cs.ed.ac.uk> scm@lfcs.ed.ac.uk (Santa C Maria) writes: >This is probably a rather silly question. I would be glad, if you >can give me a hint. I want to implement a number of loops in this >manner: > for ( i[0] = 0; i[0] < x[0]; ++i[0] ) { > for ( i[1] = 0; i[1] < x[1]; ++i[1] ) { > ...... > for ( i[m-1] = 0; i[m-1] < x[m-1]; ++i[m-1] ) { > do_something_here(); > } [...] > } > >do_something_here() is thus executed x[0]*[x[1]* ... *x[m-1] times. >The problem is that m, x[0], ... x[m-1] all depend upon run-time >values. The question is how do I code this? > >Thanks in advance for your help. Hi there, try this one: for (c= 0; c < m; i[c++]= 0); /* All i[] to zero */ while (c != -1) { do_something_here(); /* Next addition with carries */ for (c= m-1; (c != -1)&&(i[c] >= x[c]-1); c--) i[c]= 0; /* Check on overflow */ if (c != -1) i[c]++; } Hope this helps, Jos |O J.A. Horsmeier AND Software B.V. phone : +31 10 4367100 O| |O Westersingel 106/108 fax : +31 10 4367110 O| |O 3015 LD Rotterdam NL e-mail: jos@and.nl O|