EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH

Program Flow Statements

• IF

  if (logical_expression) {statement 1; statement 2; ...; statement n; }
  

  where "logical_expression" is one of

  expr1 oper expr2
  expr11 oper1 expr12 && expr21 oper2 expr22
  expr11 oper1 expr12 || expr21 oper2 expr22
  

  and oper one of

  ==          ! equal
  <>          ! not equal
  <           ! less than
  >           ! greater than
  <=          ! less than or equal
  >=          ! greater than or equal
  

  The expressions are arithmetic expressions of type real. The statements in the curly brackets are executed if the logical expression is true.

• ELSEIF

  elseif (logical_expression) {statement 1; statement 2; ...; statement n; }
  

  Only possible (in any number) behind an IF, or another ELSEIF; is executed if logical_expression is true, and if none of the preceding IF or ELSEIF logical conditions was true.

• ELSE

  else {statement 1; statement 2; ...; statement n; }
  

  Only possible (once) behind an IF, or an ELSEIF; is executed if logical_expression is true, and if none of the preceding IF or ELSEIF logical conditions was true.

  For a real life example, see ELSE example.

• WHILE

  while (logical_condition){statement 1; statement 2; ...; statement n; }
  

  executes the statements in curly brackets while the logical_expression is true. A simple example (in case you have forgotten the first ten factorials) would be

  option,-info;   ! otherwise you get redifiniton warnings
  n=1; m=1;
  while (n <= 10)
  {
    m = m * n;  value, m;
    n = n + 1;
  };
  

  For a real life example, see WHILE example.

• MACRO

label: macro = {statement 1; statement 2; ...; statement n; };
label(arg1,...,argn): macro = {statement 1; statement 2; ...; statement n; };

exec, label;

The second form allows to replace strings anywhere inside the statements in curly brackets by other strings, or integer numbers prior to execution. This is a powerful construct and should be handled with care.

Simple example:

option,-echo,-info;  ! otherwise the output is somewhat confusing
simple(xx,yy): macro = { xx = yy^2 + xx; value, xx;};
a = 3;
b = 5;
exec, simple(a,b);

Somewhat more tricky (a "$" in front of an argument means that the truncated integer value of this argument is used for replacement, rather than the argument string itself).

tricky(xx,yy,zz): macro = {mzz.yy: xx, l = 1.yy, kzz = k.yy;};
n=0;
while (n < 3)
{
  n = n+1;
  exec,tricky(quadrupole,$n,1);
  exec,tricky(sextupole,$n,2);
};

Beware of the following rules:

exec,thismacro($99,$129);

n1=99; n2=219;
exec,thismacro($n1,$n2);