Improve alt build of 1989/ovdluhe

One can now do

    make clobber P=5 alt

instead of the more awkward

    make clobber CDEFINE="-DP=5" alt

The try.alt.sh script was added and allows one to do

    P=5 ./try.alt.sh

If P is not specified it uses the default of the alt code (which checks
if it's defined first via #ifdef..#endif). Otherwise it uses the new
value. Of course if one specifies not an int or too high value (or maybe
too low - didn't try that) the program will fail. That is the fault of
the user. The author does note a reasonable range to try.

1989/ovdluhe/Makefile

@@ -140,8 +140,11 @@ ${PROG}: ${PROG}.c
 alt: data ${ALT_TARGET}
 	@${TRUE}
 
+# Variable to simplify reconfiguring P
+#
+P= '(A<<AP)'
 ${PROG}.alt: ${PROG}.alt.c
-	${CC} ${CFLAGS} $< -o $@ ${LDFLAGS}
+	${CC} ${CFLAGS} -DP=${P} $< -o $@ ${LDFLAGS}
 
 # data files
 #

1989/ovdluhe/README.md

@@ -35,11 +35,12 @@ it's a `#define` it's easy to set up.
 ### Alternate build:
 
 ```sh
-make CFLAGS="-DP=9" clobber alt
+make P=9 clobber alt
 ```
 
 You do not have to define `P` but if you do you can replace the value with
-whatever you wish, as long as it's an int.
+whatever you wish, as long as it's an int (or evaluates to an int like the
+default `(A<<AP)` does).
 
 
 ### Alternate use:
@@ -48,6 +49,16 @@ whatever you wish, as long as it's an int.
 ./ovdluhe.alt
 ```
 
+### Alternate try:
+
+```sh
+./try.alt.sh
+
+P=5 ./try.alt.sh
+```
+
+NOTE: if you specify too high a value for `P` the program might fail.
+
 
 ## Judges' remarks:
 

1989/ovdluhe/try.alt.sh

@@ -0,0 +1,38 @@
+#!/usr/bin/env bash
+#
+# try.alt.sh - demonstrate IOCCC winner 1989/ovdluhe.alt alt code
+#
+
+# make sure CC is set so that when we do make CC="$CC" it isn't empty. Doing it
+# this way allows us to have the user specify a different compiler in an easy
+# way.
+if [[ -z "$CC" ]]; then
+    CC="cc"
+fi
+
+# user may also reconfigure P
+if [[ -n "$P" ]]; then
+    make clobber CC="$CC" P="$P" alt >/dev/null || exit 1
+else
+    make clobber CC="$CC" alt >/dev/null || exit 1
+fi
+
+# clear screen after compilation so that only the entry is shown
+
+i=0
+for ((i=0; i<4; ++i)); do
+    read -r -n 1 -p "Press any key to run: ./ovdluhe.alt < ovdluhe.alt.c: "
+    echo 1>&2
+    ./ovdluhe.alt < ovdluhe.alt.c
+    echo 1>&2
+
+    read -r -n 1 -p "Press any key to run: ./ovdluhe.alt < README.md: "
+    echo 1>&2
+    ./ovdluhe.alt < README.md
+    echo 1>&2
+
+    read -r -n 1 -p "Press any key to run: ./ovdluhe.alt < Makefile: "
+    echo 1>&2
+    ./ovdluhe.alt < Makefile
+    echo 1>&2
+done