Branching Constructs

[ The if statement ] [ The if-then-else statement ]

The if and if-then-else statements provide branching control in ALADDIN's problem solving procedures.

THE if STATEMENT

Syntax : The if statement syntax is:

    if ( logical expression ) {
         statement 1 ;
         statement 2 ;
         ......
         statement N ;
    }

Statements 1 through N will be executed only if the logical expression evaluates to "true." Readers should also note that unlike the C programming language, the braces are required even if N equals 1.

Example 1 : The script

    x = 1 ksi;                  
    if ( x < 10 ksi ) {
         print " x = ", x ,"\n";
    }

generates the output

    x =      1 ksi

Example 2 : Logical expressions can be a composition of logical and relational operands. For example, the script:

    time = 20 sec;
  
    if( time > 0 sec && time <= 100 sec ) {
        print " time = ", time, "\n";
    }

    time =       20 sec 

Example 3 : ALADDIN checks compatibility of units before attempting to evaluate the logical expression. The run-time execution of the script

    x = 1 ksi;                  
    if ( x < 10 cm ) {
         print " x = ", x ,"\n";
    }

THE if-then-else STATEMENT

Syntax : The if-then-else statement syntax is:

    if ( logical expression ) then {
         statement 1 ;
         ......
         statement K ;
    } else {
         statement K+1 ;
         ......
         statement N ;
    }

Statements 1 through K will be executed if the logical expression evaluates to "true." Otherwise, statements K+1 through N will be executed.

Example 4 : The script

    x = 10 ksi; y = 1 MPa;
    if ( x < 10 ksi ) then {
         print " x = ", x ,"\n";
    } else {
         print " y = ", y ,"\n";                    
    }

generates the output

    y =        1 MPa