Unconditional branch

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We can use goto statements (unconditional branch statements) to jump to a label in a program. In C++ and Pascal, a label is specified by an identifier (the name of the label) followed by a colon (:). However, labels in a Pascal program should be declared with the reserved word label, while labels in C++ programs need not be declared.

The following program makes use of an unconditional branch to draw an inverted triangle with asterisks (*). However, the number of rows is limited to 10 or less.

Program 22: Using unconditional jumps
C++ version Pascal version
#include <iostream.h>
main()
{
  int i, j, n;

  cout << "n? ";
  cin >> n;
  for (i = 1; i <= n; i++) {
    if (i > 10)
      goto finished;
    for (j = n; j >= i; j--)
      cout << "* ";
    cout << endl;
  }
finished:
  cout << "Finished!" << endl;

  return 0;
}		 program prog_22(input, output);
label finished;
var
  i, j, n: integer;
begin
  write('n? ');
  readln(n);
  for i := 1 to n do begin
    if i > 10 then
      goto finished;
    for j := n downto i do
      write('* ');
    writeln
  end;
finished:
  writeln('Finished!')
end.
Sample output 1 (text in red is entered by user):
n? 8
* * * * * * * *
* * * * * * *
* * * * * *
* * * * *
* * * *
* * *
* *
*
Finished!
Sample output 2 (text in red is entered by user):
n? 15
* * * * * * * * * * * * * * *
* * * * * * * * * * * * * *
* * * * * * * * * * * * *
* * * * * * * * * * * *
* * * * * * * * * * *
* * * * * * * * * *
* * * * * * * * *
* * * * * * * *
* * * * * * *
* * * * * *
Finished!

Although using unconditional branches is quite convenient, it is not preferable. In practice, it is almost always easy to write code without unconditional branches. For example, the shaded part of the above program can be written as follows:

Program 23: Re-writing Program 22 without using unconditional branches
C++ version Pascal version
#include <iostream.h>
main() {
  int i, j, n;

  cout << "n? ";
  cin >> n;
  i = 1;
  while ((i <= n) && (i <= 10)) {
    for (j = n; j >= i; j--)
      cout << "* ";
    cout << endl;
    i++;
  }
  cout << "Finished!" << endl;

  return 0;
}		 program prog_23(input, output);
var
  i, j, n: integer;
begin
  write('n? ');
  readln(n);
  i := 1;
  while (i <= n) and (i <= 10) do begin
    for j := n downto i do
      write('* ');
    writeln;
    i := i + 1
  end;
  writeln('Finished!')
end.

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