Rewrite Pascal for do loop using while do loop

Question

Please how do I rewrite the below FOR....DO loop into a WHILE...DO loop in Pascal programming

Below is the following code

Program Matmuli(input,output);

:

:

FOR i:=1 TO m DO

  FOR j:=1 TO p DO

     BEGIN
    
        C[i,j]:= 0.0;
        FOR k:=1 TO n DO
          C[i,j]:= C[i,j] + A[i,k] * B[k,j];

     END;

`for i := a to b do P(i)` is the same as `i := a; while i <= b do begin P(i); Inc(i); end`. Use that three times. — Andreas Rejbrand, Feb 20 '21 at 12:05
Thanks bro.. which is better to loop through what I have above and why do you feel the one you say is best.. — Browyn Louis, Feb 20 '21 at 13:28
The `for` loop is the better choice in this case because it (clearly) is less code (and so easier to see and interpret mentally, less room for typos etc.). — Andreas Rejbrand, Feb 20 '21 at 13:29
...moreover, in some (all?) pascal implementation, the for limit is calculated only once, not at every iteration. — linuxfan says Reinstate Monica, Feb 26 '21 at 11:31

score 0 · Answer 1 · answered Aug 13 '21 at 06:37

The for loop is well defined in terms of a while loop, confer ISO 7185 “Standard Pascal”, quote:

Apart from the restrictions imposed by these requirements, the for-statement
for v := e1 to e2 do body
shall be equivalent to
begin
  temp1 := e1;
  temp2 := e2;
  if temp1 <= temp2 then
    begin
      v := temp1;
      body;
      while v <> temp2 do
        begin
          v := succ(v);
          body
        end
    end
end
[…]

where temp1 and temp2 denote auxiliary variables that the program does not otherwise contain, and that possess the type possessed by the variable v […]

The important thing from this expanded piece of code is, as linuxfan says Reinstate Monica already noted, that in Pascal the limits of a for loop are only evaluated once. Furthermore, the control-variable is only assigned a value if there was indeed at least one iteration.

However, usually it’s sufficient to transform a for loop as Andreas Rejbrand already suggested, although it is technically not the same.

Rewrite Pascal for do loop using while do loop

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