Document revision date: 30 March 2001

## OpenVMS Debugger Manual

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### C.17.2 Constructs in Language and Address Expressions

Supported constructs in language and address expressions for language UNKNOWN follow:

Symbol | Construct
--- | ---
[ ] | Subscripting
( ) | Subscripting
. (period) | Record component selection
^ (circumflex) | Pointer dereferencing

### C.17.3 Predefined Symbols

Supported predefined symbols for language UNKNOWN follow:

Symbol | Meaning
--- | ---
TRUE | Boolean True
FALSE | Boolean False
NIL | Nil pointer

### C.17.4 Data Types

When the language is set to UNKNOWN, the debugger understands all data types accepted by other languages except a few very language-specific types, such as picture types and file types. In UNKNOWN language expressions, the debugger accepts most scalar OpenVMS calling standard data types.

- For language UNKNOWN, the debugger accepts the dot-notation for record component selection. For example, if C is a component of a record B which in turn is a component of a record A, then C can be referenced as A.B.C. Subscripts can be attached to any array components; for example, if B is an array, then C can be referenced as A.B[2,3].C.
- For language UNKNOWN, the debugger accepts brackets and parentheses for subscripts. For example, A[2,3] and A(2,3) are equivalent.

## Appendix D
EIGHTQUEENS.C

This appendix contains the source code for the programs used in many figures of Chapter 8, Chapter 9, and Chapter 10, EIGHTQUEENS.C AND 8QUEENS.C. These programs are presented here only to assist in understanding the procedures described in those chapters.

## D.1 EIGHTQUEENS.C

Example D-1 contains EIGHTQUEENS.C, the single-module program that solves the eightqueens problem.

Example D-1 Single-Module Program EIGHTQUEENS.C

    extern void setqueen();
    extern void removequeen();
    extern void trycol();
    extern void print();
        int a[8];     /* a : array[1..8]  of boolean */
        int b[16];    /* b : array[2..16] of boolean */
        int c[15];    /* c : array[-7..7] of boolean */
        int x[8];

    /* Solve eight-queens problem */
    main()
    {
        int i;
        for (i=0; i <=7; i++)
     a[i] = 1;
        for (i=0; i <=15; i++)
     b[i] = 1;
        for (i=0; i <=14; i++)
     c[i] = 1;
        trycol( 0 );
    } /* End main */

    void trycol( j )
        int j;
    {
        int m;
        int safe;
        m = -1;
        while (m++ < 7)
           {
           safe = (a[m] ==1) && (b[m + j] == 1) && (c[m - j + 7] ==1);
           if (safe)
                {
         setqueen(m, j);
         x[j] = m + 1;
         if (j < 7)
      trycol(j + 1);
         else
      print();
         removequeen(m, j);
         }
           }
    } /* End trycol */

    void setqueen(m, j)
        int m;
        int j;
    {
        a[m] = 0;
        b[m + j] = 0;
        c[m - j + 7] = 0;
    } /* End setqueen */

    void removequeen(m, j)
        int m;
        int j;
    {
        a[m] = 1;
        b[m + j] = 1;
        c[m - j + 7] = 1;
    } /* End removequeen */

    void print()
    {
        int k;
        for (k=0; k<=7; k++)
     {
     printf(" %d", x[k]);
     }
        printf("\n");
    } /* End print */

## D.2 8QUEENS.C

8QUEENS.C is the multiple-module program that solves the eightqueens problem. This program consists of two modules, 8QUEENS.C (Example D_2) and 8QUEENS_SUB.C (Example D-3).

Example D-2 Main Module 8QUEENS.C

    extern void trycol();
        int a[8];     /* a : array[1..8]  of boolean */
        int b[16];    /* b : array[2..16] of boolean */
        int c[15];    /* c : array[-7..7] of boolean */
        int x[8];

    main()    /* Solve eight-queens problem */
    {
        int i;
        for (i=0; i <=7; i++)
     a[i] = 1;
        for (i=0; i <=15; i++)
     b[i] = 1;
        for (i=0; i <=14; i++)
     c[i] = 1;
        trycol(0);
        printf(" Solved eight-queens problem!\n");
    } /* End main */

Example D-3 Submodule 8QUEENS_SUB.C

    extern int a[8];
    extern int b[16];
    extern int c[15];
    extern void setqueen();
    extern void removequeen();
    extern void print();

        int x[8];

    void trycol( j )
        int j;
    {
        int m;
        int safe;
        m = -1;
        while (m++ < 7)
           {
           safe = (a[m] ==1) && (b[m + j] == 1) && (c[m - j + 7] ==1);
           if (safe)
                {
                setqueen(m, j);
                x[j] = m + 1;
                if (j < 7)
                    trycol(j + 1);
                else
                    print();
                removequeen(m, j);
                }
           }
    }       /* End trycol */

    void setqueen(m, j)
        int m;
        int j;
    {
        a[m] = 0;
        b[m + j] = 0;
        c[m - j + 7] = 0;
    }       /* End setqueen */

    void removequeen(m, j)
        int m;
        int j;
    {
        a[m] = 1;
        b[m + j] = 1;
        c[m - j + 7] = 1;
    }       /* End removequeen */

    void print()
    {
        int k;
        for (k=0; k<=7; k++)
            {
            printf(" %d", x[k]);
            }
        printf("\n");
    }       /* End print */

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