The Alternative Csound Reference Manual
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# Writing a Main Program

The general format for a control program is:

    #include  "cscore.h"
    cscore()
    {
     /*  VARIABLE DECLARATIONS  */
     /*  PROGRAM BODY  */
    }

The include statement will define the event and list structures for the program. The following C program will read from a standard numeric score, up to (but not including) the first s or e statement, then write that data (unaltered) as output.

    #include  "cscore.h"
    cscore()
    {
         EVLIST *a;       /* a is allowed to point to an event list */
         a = lget();      /* read events in, return the list pointer */
         lput(a);         /* write these events out (unchanged) */
         putstr("e");     /* write the string e to output */
    }

After execution of lget(), the variable a points to a list of event addresses, each of which points to a stored event. We have used that same pointer to enable another list function (lput) to access and write out all of the events that were read. If we now define another symbol e to be an event pointer, then the statement

    e = a-e[4];

will set it to the contents of the 4th slot in the evlist structure. The contents is a pointer to an event, which is itself comprised of an array of parameter field values. Thus the term e-p[5] will mean the value of parameter field 5 of the 4th event in the evlist denoted by a. The program below will multiply the value of that pfield by 2 before writing it out.

    #include  "cscore.h"
    cscore()
    {
         EVENT  *e;       /* a pointer to an event   */
         EVLIST *a;
         a = lget();      /* read a score as a list of events */
         e = a-e[4];     /* point to event 4 in event list a  */
         e-p[5] *= 2;    /* find pfield 5, multiply its value by 2 */
         lput(a);         /* write out the list of events  */
         putstr("e");     /* add a "score end" statement */
    }

Now consider the following score, in which p[5] contains frequency in Hz.

    f 1 0 257 10 1
    f 2 0 257 7 0 300 1 212 .8
    i 1 1 3 0 440 10000
    i 1 4 3 0 256 10000
    i 1 7 3 0 880 10000
    e

If this score were given to the preceding main program, the resulting output would look like this:

    f 1 0 257 10 1
    f 2 0 257 7 0 300 1 212 .8
    i 1 1 3 0 440 10000
    i 1 4 3 0 512 10000        ; p[5] has become 512 instead of 256.
    i 1 7 3 0 880 10000
    e

Note that the 4th event is in fact the second note of the score. So far we have not distinguished between notes and function table setup in a numeric score. Both can be classed as events. Also note that our 4th event has been stored in e[4] of the structure. For compatibility with Csound pfield notation, we will ignore p[0] and e[0] of the event and list structures, storing p1 in p[1], event 1 in e[1], etc. The Cscore functions all adopt this convention.

As an extension to the above, we could decide to use a and e to examine each of the events in the list. Note that e has not preserved the numeral 4, but the contents of that slot. To inspect p5 of the previous listed event we need only redefine e with the assignment

    e = a-e[3];

More generally, if we declare a new variable f to be a pointer to a pointer to an event, the statement

    f = &a-e[4];

will set f to the address of the fourth event in the event list a, and *f will signify the contents of the slot, namely the event pointer itself. The expression

    (*f)-p[5],

like e-p[5], signifies the fifth pfield of the selected event. However, we can advance to the next slot in the evlist by advancing the pointer f. In C this is denoted by f++.

In the following program we will use the same input score. This time we will separate the ftable statements from the note statements. We will next write the three note-events stored in the list a, then create a second score section consisting of the original pitch set and a transposed version of itself. This will bring about an octave doubling.

By pointing the variable f to the first note-event and incrementing f inside a while block which iterates n times (the number of events in the list), one statement can be made to act upon the same pfield of each successive event.

    #include  "cscore.h"
     cscore()
     {
          EVENT *e,**f;            /* declarations. see pp.8-9 in the */
          EVLIST *a,*b;            /* C language programming manual */
          int n;
          a = lget();              /* read score into event list "a" */
          b = lsepf(a);            /* separate f statements */
          lput(b);                 /* write f statements out to score */
          lrelev(b);               /* and release the spaces used */
          e = defev("t 0 120");    /* define event for tempo statement */
          putev(e);                /* write tempo statement to score */
          lput(a);                 /* write the notes */
          putstr("s");             /* section end */
          putev(e);                /* write tempo statement again */
          b = lcopyev(a);          /* make a copy of the notes in "a" */
          n = b-nevents;          /* and get the number present */
          f = &a-e[1];
          while (n--)              /* iterate the following line n times: */
              (*f++)-p[5] *= .5;  /*   transpose pitch down one octave */
          a = lcat(b,a);           /* now add these notes to original pitches */
          lput(a);
          putstr("e");
         }

The output of this program is:

    f 1 0 257 10 1
    f 2 0 257 7 0 300 1 212 .8
    t 0 120
    i 1 1 3 0 440 10000
    i 1 4 3 0 256 10000
    i 1 7 3 0 880 10000
    s
    t 0 120
    i 1 1 3 0 440 10000
    i 1 4 3 0 256 10000
    i 1 7 3 0 880 10000
    i 1 1 3 0 220 10000
    i 1 4 3 0 128 10000
    i 1 7 3 0 440 10000
    e

Next we extend the above program by using the while statement to look at p[5] and p[6]. In the original score p[6] denotes amplitude. To create a diminuendo in the added lower octave, which is independent from the original set of notes, a variable called dim will be used.

    #include "cscore.h"
    cscore()
    {
      EVENT *e,**f;
      EVLIST *a,*b;
      int n, dim;                /* declare two integer variables   */
      a = lget();
      b = lsepf(a);
      lput(b);
      lrelev(b);
      e = defev("t 0 120");
      putev(e);
      lput(a);
      putstr("s");
      putev(e);                  /* write out another tempo statement */
      b = lcopyev(a);
      n = b-nevents;
      dim = 0;                   /* initialize dim to 0 */
      f = &a-e[1];
      while (n--){
           (*f)-p[6] -= dim;    /* subtract current value of dim */
           (*f++)-p[5] *= .5;   /* transpose, move f to next event */
           dim += 2000;          /* increase dim for each note */
      }
      a = lcat(b,a);
      lput(a);
      putstr("e");
    }

The increment of f in the above programs has depended on certain precedence rules of C. Although this keeps the code tight, the practice can be dangerous for beginners. Incrementing may alternately be written as a separate statement to make it more clear.

    while (n--){
         (*f)-p[6] -= dim;
         (*f)-p[5] *= .5;
         dim += 2000;
         f++;
    }

Using the same input score again, the output from this program is:

    f 1 0 257 10 1
    f 2 0 257 7 0 300 1 212 .8
    t 0 120
    i 1 1 3 0 440 10000
    i 1 4 3 0 256 10000
    i 1 7 3 0 880 10000
    s
    t 0 120
    i 1 1 3 0 440 10000     ; Three original notes at
    i 1 4 3 0 256 10000     ; beats 1,4 and 7 with no dim.
    i 1 7 3 0 880 10000
    i 1 1 3 0 220 10000     ; three notes transposed down one octave
    i 1 4 3 0 128 8000      ; also at beats 1,4 and 7 with dim.
    i 1 7 3 0 440 6000
    e

In the following program the same three-note sequence will be repeated at various time intervals. The starting time of each group is determined by the values of the array cue. This time the dim will occur for each group of notes rather than each note. Note the position of the statement which increments the variable dim outside the inner while block.

    #include  "cscore.h"
    int cue[3]={0,10,17};              /* declare an array of 3 integers */
    cscore()
    {
         EVENT *e, **f;
         EVLIST *a, *b;
         int n, dim, cuecount, holdn;  /* declare new variables */
         a = lget();
         b = lsepf(a);
         lput(b);
         lrelev(b);
         e = defev("t 0 120");
         putev(e);
         n = a-nevents;
         holdn = n;                    /* hold the value of "n" to reset below */
         cuecount = 0;                 /* initialize cuecount to "0" */
         dim = 0;
         while (cuecount <= 2) {       /* count 3 iterations of inner "while" */
              f = &a-e[1];            /* reset pointer to first event of list "a" */
              n = holdn;               /* reset value of "n" to original note count */
              while (n--) {
                  (*f)-p[6] -= dim;
                  (*f)-p[2] += cue[cuecount];   /* add values of cue */
                  f++;
              }
              printf("; diagnostic:  cue = %d\n", cue[cuecount]);
              cuecount++;
              dim += 2000;
               lput(a);
         }
         putstr("e");
    }

Here the inner while block looks at the events of list a (the notes) and the outer while block looks at each repetition of the events of list a (the pitch group repetitions). This program also demonstrates a useful trouble-shooting device with the printf function. The semi-colon is first in the character string to produce a comment statement in the resulting score file. In this case the value of cue is being printed in the output to insure that the program is taking the proper array member at the proper time. When output data is wrong or error messages are encountered, the printf function can help to pinpoint the problem.

Using the identical input file, the C program above will generate:

    f 1 0 257 10 1
    f 2 0 257 7 0 300 1 212 .8
    t 0 120
    ; diagnostic:  cue = 0
    i 1 1 3 0 440 10000
    i 1 4 3 0 256 10000
    i 1 7 3 0 880 10000
    ; diagnostic:  cue = 10
    i 1 11 3 0 440 8000
    i 1 14 3 0 256 8000
    i 1 17 3 0 880 8000
    ; diagnostic:  cue = 17
    i 1 28 3 0 440 4000
    i 1 31 3 0 256 4000
    i 1 34 3 0 880 4000
    e;

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