Page 145 - Standard Handbook Of Petroleum & Natural Gas Engineering

130 Mathematics

Iterative statements control how many times a simple statement or a com-
pound statement is repeated, and also may be nested with conditional and/or
other iterative statements. They may be
WHILE boolean expression DO
statement

or
REPEAT
statement
UNTIL boolean expression

or
FOR variable: = expression TO expression DO
statement

where the variable and expressions must be of ordinal (not real) type and TO
may be replaced by DOWNTO. In all types of iterative constructions, statement
may refer to a simple statement or to a compound statement introduced by
BEGIN and completed with END, for example,

WHILE NOT EOF DO
BEGIN
I: = 0;
REPEAT
I: = I + 1;
READ(TEMP( I))
UNTIL I > MAXI
END;
FOR I: = MAXI DOWNTO MINI DO
BEGIN
X(1): = FNC(X(1 - 1) * ABS(Z);
IF X(1) > XFT THEN AGSTP(X(I),I,PTP(I))
END;
Subprogram statements-Used to transfer control between program units-the
main program, functions, and procedures. A function call is the invocation of a
function name in an assignment statement, such as
X: = DEF(Y)*Z;
which will transfer control to DEF and pass the variable Y to that function.
Control returns to the calling unit when the END statement of the function is
encountered. Intrinsic functions, supplied in the system library, are called in the
same manner. (See Table 1-30 for a list of standard Pascal intrinsic functions.)
A procedure call is made by stating the name of the procedure and the variables
to be passed, e.g.,
CALCPRSSR( PIPENUM,TEMP,FFACTR);
will transfer control to procedure CALCPRSSR. Control returns to the calling
unit when the procedure END statement is found.