**Tcl Learning Exercises: Answer: Number Sign Class**

Write a procedure that takes one argument, a number, and returns -1, 0, or 1, indicating that the number is negative, zero, or positive, respectively. The procedure may contain exactly one command, expr, which may use the *if-then-else* (?...:) operator at most one time. **Bonus Round:** Add an additional constraint: The *if-then-else* operator may not be used.

Here is one answer:

proc numsign n {expr {$n == 0 ? 0 : $n/abs($n)}}

Scroll down for the bonus round answer...

Here is a solution by rmax to the bonus round:

proc numsign n {expr {($n > 0) - ($n < 0)}}

AMG: While this may be an interesting beginner problem, I don't think it succeeds in demonstrating anything special about Tcl other than that math must be done using [expr]. Text manipulation problems will likely do better to motivate interest in Tcl.

RKZn 2017-05-27: Actually there is a subtle difference in the two procs. The return value of first one (with the ?: operator) is represented as an integer or a double, depending on the input's representation. The second proc always returns a integer representation.

tcl> info patch 8.6.1 tcl> proc numsign n {expr {$n == 0 ? 0 : $n/abs($n)}} tcl> tcl::unsupported::representation [numsign -5] value is a int with a refcount of 1, object pointer at 0xb507f0, internal representation 0xffffffffffffffff:0xb53250, no string representation tcl> tcl::unsupported::representation [numsign -5.5] value is a double with a refcount of 1, object pointer at 0x91a210, internal representation 0xbff0000000000000:0xb50ee0, no string representation tcl> proc numsign n {expr {($n > 0) - ($n < 0)}} tcl> tcl::unsupported::representation [numsign -5] value is a int with a refcount of 1, object pointer at 0x919c40, internal representation 0xffffffffffffffff:0xb50880, no string representation tcl> tcl::unsupported::representation [numsign -5.5] value is a int with a refcount of 1, object pointer at 0xb50ee0, internal representation 0xffffffffffffffff:0xb53130, no string representation

Other ways to do it from my own post on Code Golf - Output the sign :

puts [expr $n<0?-1:$n>0]

puts [expr !!$n|$n>>31]