Clojure (74 characters)

Guessing a real number. Nobody will be patient enought to solve to "=", so nobody notice the missing exit.

java -jar clojure.jar  -e "(loop[n(rand)](prn (get{-1 '+ 0 '= 1 '-}(compare(eval(read))n)))(recur n))"
0.5
+
0.8
-
0.6
+
0.7
+
0.75
-
0.72
+
0.74
+
0.745
+
0.748
-
0.746
-
0.7455
-
...

Clojure (117 characters)

java -jar clojure.jar  -e "(loop[n(int(*(rand 100)))]((get{-1#(prn '+)0#(do(prn '=)(System/exit 0))1#(prn '-)}(compare(eval(read))n)))(recur n))"
50
+
75
+
90
-
86
-
82
=

Clojure (74 characters)

Guessing a real number. Nobody will be patient enought to solve to "=", so nobody notice the missing exit.

java -jar clojure.jar  -e "(loop[n(rand)](prn (get{-1 '+ 0 '= 1 '-}(compare(eval(read))n)))(recur n))"
0.5
+
0.8
-
0.6
+
0.7
+
0.75
-
0.72
+
0.74
+
0.745
+
0.748
-
0.746
-
0.7455
-
...