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Bartels User Language - Programmer's Guide

2.1 Introducing User Language Programming

Bartels AutoEngineer® Documentation

This section provides small programming examples in order to introduce the most important elements of the Bartels User Language. The purpose thereby is to demonstrate - without entering into formal details or describing exceptions - the basic methods of developing User Language programs.


2.1.1 The first User Language Program

The only way to learn how to use the User Language is by doing it, i.e., write User Language programs, and compile and execute them. The first User Language program to be implemented should print a message, and then wait for an interactive keyboard input to abort the program (this is a frequently required programming feature). As already mentioned in the introduction, an User Language program must at least contain a main function. What we need in this main function are instructions for printing the desired message and for activating the requested user query. Both of these instructions can be realized by calling corresponding User Language system functions (printf and askstr). These system functions are known to the User Language Compiler, and they are bound to the Bartels User Language Interpreter. The programmer just has to know, how these functions are to be called, and what they do (this information can be taken from appendix C of this manual). You should now use your editor for preparing a file named ulprog.ulc with the following User Language source code (the .ulc file name extension is used by the User Language Compiler for User Language source code file recognition):

      printf("User Language Program");
      askstr("Press ENTER to continue ",1);

The above listed User Language program does just contain the definition of the function main. Parentheses are required after the function name. Usually, formal function parameters are listed inside these parentheses. To distinguish function names from variable names, the parentheses are required even if (as in the example above) no function parameter exists at all. Within the braces the function block is defined. The function block is composed of the statements to be executed by the function. Each statement must be delimited by a semicolon (;). The first statement of the main function is the call to the printf function (to be recognized by the opening parenthesis after the function name). The parameter which is passed to the printf function is a constant string (enclosed by double quotes). This string is the message, which the program will print to the screen when executed after faultless compilation. The second statement is a call to the function askstr. This function issues the prompt string, which is specified with the first function parameter, and waits for an interactive string input. The user interaction takes place in the status line of the Bartels AutoEngineer, and the second askstr parameter indicates the maximum permissible input string length. The askstr call is the last statement to be processed by the program, i.e., the program finishes after executing the askstr call. Once the program source code is edited and stored to ulprog.ulc, it can be translated with the following User Language Compiler call:

ulc ulprog

The User Language Compiler issues the following message, if no compilation error occurred:


Compiling source code file "ulprog.ulc"...
Program 'ulprog' successfully created.
Source code file "ulprog.ulc" successfully compiled.

No errors, no warnings.
User Language Compilation successfully done.

Once the User Language Compiler program source code has been translated, and the corresponding machine program named ulprog has been stored to the ulcprog.vdb file of the Bartels AutoEngineer programs directory, the program can be executed by the Bartels User Language Interpreter. This can be applied e.g., by starting the Bartels AutoEngineer Schematic Editor and by activating the Run User Script function from the File menu. The program name (ulprog) must be specified to the corresponding query:

FileLeft Mouse Button (LMB)
Run User ScriptLeft Mouse Button (LMB)
Program Name ?ulprog Return/Enter Key (CR)

After starting the program, the BAE graphic workspace is switched to text output mode, and the User Language Program message is printed to the screen. Subsequently, the Press ENTER to continue prompt is displayed in the BAE input window. Return key input terminates the User Language program and restores the graphic workspace.


2.1.2 Variables, Arithmetic and Functions

The next example illustrates a series of further specific User Language characteristics. The following User Language program examines some circles (specified by center point and radius) to check whether they overlap (drill data test?!), and issues corresponding messages:

// Circle Test Program

double tol=0.254*5;           // Tolerance

struct pos {                  // Position descriptor
      double x;               // X coordinate
      double y;               // Y coordinate

struct circle {               // Circle descriptor
      double rad;             // Circle radius
      struct pos c;           // Circle position

// Main program
      // Define three circles
      struct circle c1 = {  4.5, { 19.4, 28.3} };
      struct circle c2 = { 17.0, { 37.6, 9.71} };
      struct circle c3 = { 1.5E01, { 25, 0.2e2} };
      // Perform circle test
      printf("Circle 1 - 2 overlap : %d\n",circletest(c1,c2));
      printf("Circle 1 - 3 overlap : %d\n",circletest(c1,c3));
      printf("Circle 2 - 3 overlap : %d\n",circletest(c2,c3));
      // Prompt for continue
      askstr("Press ENTER to continue ",1);

int circletest(c1,c2)
// Circle test function
// Returns: nonzero if overlapping or zero else
struct circle c1,c2           /* Test circles 1 and 2 */;
      double d                /* Distance value */;
      // Get circle center point distances
      // Error tolerant check distance against radius sum

double distance(p1,p2)
// Get distance between two points
// Returns: distance length value
struct pos p1                 /* Point 1 */;
struct pos p2                 /* Point 2 */;
      double xd=p2.x-p1.x     /* X distance */;
      double yd=p2.y-p1.y     /* Y distance */;
      // Calculate and return distance

The above listed program source code contains a series of comments enclosed by /* and */; such comments can extend over several lines, but they must not nest. Another type of comment starts with // and extents to the end of line. Since comments can keep the program source code well understandable, it is recommended to use such inline documentation to simplify User Language software maintenance.

The program above also contains a series of variable definitions. All variables must be declared before use. A variable declaration determines the name and the data type of the variable. Bartels User Language distinguishes between global variables, local variables and function parameters. Global variables are valid throughout the entire program text. Local variables are valid in the function where they are defined. Function parameters are used for passing values to functions. In the example above, tol is the only global variable (with data type double). Local variables are, e.g., xd and yd (data type double) in the distance function. Function parameters are, e.g., c1 and c2 in the circletest function; these two parameters are of the specially defined combined struct circle data type. Variable declarations can contain variable value initializations (see the global variable tol or the local variables xd and yd in the distance function). Combined data type variables can be initialized (see the local struct variables c1, c2 and c3 in the main function). A list of variable names can be specified at the declaration of variables (see the declaration of the parameters c1 and c2 in the circletest function).

Values are calculated within expressions. The equals sign (=) can be used for assigning the resulting expression value to a variable.

A data type must be specified at the definition of functions. In the example above, the distance function is of type double, and the circletest function is of type int. The function data type is set to int if the function data type specification is omitted (as with the main function in the example above). A special function data type is void. Each function - except for the void functions - returns a value compatible to the corresponding function data type. The function return value is passed back to the caller of the function with the return statement, which is coincidentally the last instruction to be executed by the function.


2.1.3 Arrays and Control Structures

The following example shows how to use arrays and control structures. A list of integer values are transformed into strings, and a report of the transformations is printed:

// Integer list
int intary[]={ 0,17,-12013,629,0770,0xFF,-16*4+12 };

// Main program
      int i                   /* Loop control variable */;
      // Set last integer value
      // Loop through integer list
      for (i=0;i<=10;i++)
              // Print integer and integer string
              printf("%8d : \"%s\"\n",intary[i],inttostr(intary[i]));
      // Prompt for continue
      askstr("Press ENTER to continue ",1);

string inttostr(int intval)
// Convert integer value to a string
// Returns: resulting string
      string resstr=""        /* Result string */;
      int n=intval,i=0        /* Integer value, loop counter */;
      char sign               /* Sign character */;
      // Test for negative integer value
      if (n==0)
              // Return zero integer string
      else if (n>0)
              // Set sign to plus character
      else {
              // Make integer value positive
              // Set sign to minus character
      // Build result string
      do {    // Get and append next character
              } while ((n/=10)!=0);
      // Append zeros
      while (i++<15)
      // Append sign character
      // Reverse string
      // Return string result

In the example above, an integer array (global int variable intary) is declared and (partially) initialized. The bracket pair after the variable name intary defines an one-dimensional int vector. Multiple vector dimensions can be specified by appending further bracket pairs to the declaration (intary[][]...[]). Since the User Language provides powerful in-build features for dynamically managing arrays, it is not necessary, to define array length limits; i.e., both the User Language Compiler and the Bartels User Language Interpreter require just the information about the dimension of an array and/or vector. Nevertheless some checks are applied in order to prevent from accessing non-existent array elements (which would cause memory protection faults); the Compiler is able to check for constant negative (i.e., invalid) array indices, and the Interpreter is able to check whether an array index refers to an array element outside the currently engaged array field range. The array index value 0 always refers to the first array element.

The string data type corresponds to an one-dimensional array of type char. User Language provides in-build features for the direct assignment of arrays and/or vectors with corresponding data type and equal dimension. These features have been utilized at the initialization of resstr (local string variable of the inttostr function) as well as with the assignment of the return value of the inttostr function. The add operator can also be applied to string values, with the result of the add operation corresponding to a string catenation.

The example above contains some control structures. A for loop for processing the elements of the intary array variable is applied in the main function. The inttostr function uses a while loop and a do-while loop for manipulating the resstr string variable. The inttostr function utilizes an if control structure to process dependent program blocks according to the current value of local variable n.

Baumeister Mediasoft Engineering » Bartels AutoEngineer » BAE Documentation » User Language Programmer's Guide » Language Description » Introducing User Language Programming

Introducing User Language Programming • © 1985-2024 Oliver Bartels F+E • Updated: 29 October 2008, 12:56 [UTC]

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Introducing User Language Programming - English Version Einführung in die User Language Programmierung - Deutsche Version