Tcl Switch case error ,I need proper explanation for the error - switch-statement

Question

Kindly help me detecting the error in the following code
proc strcmp { d1 d2 } {
set res [string compare $d1 $d2]
switch $res
0 {
puts "String is equal "
}
1 {
puts "$d1 > $d2"
} default {
puts "$d2 > $d1"
}
}
I get this error message when i try to execute in tcl 8.5
wrong # args: should be "switch ?switches? string pattern body ... ?default body?"

Answer 1

You have the "0" on a different line. Tcl treats newlines as command terminators. You're probably seeing an error like "0: no such command"
Use either line continuations
switch $res \
0 {
puts "String is equal "
} \
1 {
puts "$d1 > $d2"
} \
default {
puts "$d2 > $d1"
}
or enclosing brackets (good for readability)
switch $res {
0 {
puts "String is equal "
}
1 {
puts "$d1 > $d2"
}
default {
puts "$d2 > $d1"
}
}
Docs:
http://tcl.tk/man/tcl8.6/TclCmd/Tcl.htm (rules 1 and 9)
http://tcl.tk/man/tcl8.6/TclCmd/switch.htm

Answer 2

The exact error I got when I tried to run your code was:
bad option "-1": must be -exact, -glob, -regexp, or -- while executing
The Tcl docs for switch mention these commands: they tell the switch how to match the arguments. Adding -exact -- before $res at the start of the switch statement seems to make it work:
proc strcmp { d1 d2 } {
set res [string compare $d1 $d2]
switch -exact -- $res {
0 {
puts "String is equal "
}
1 {
puts "$d1 > $d2"
}
default {
puts "$d2 > $d1"
}
}
}
strcmp "world" "hello"
strcmp "hello" "hello"
strcmp "hello" "world"
(You could drop the -exact if you want, as it's the default – I only include it so you can see where to put in another option.)
This gives the following output (codepad example):
world > hello
String is equal
world > hello
so for some reason, -1 (the return code from string compare for the third example) is getting matched to 1 by the switch statement. I don't know enough Tcl to know why that might be the case – you could consider asking that as a different question.