Example 12: Check If A Number Is A Prime Number

#!/usr/bin/tclsh

puts "Enter the number: "
gets stdin input

proc checkPrime {number} {
	set flag 0
	set part [expr int(sqrt($number))]
	for {set i 2} {$i <= $part} {incr i} {
		if {[expr $number % $i] == 0} {
			set flag 1
			break
		}
	}
	return $flag
}

if {[checkPrime $input] == 1} {
	puts "$input is not a prime number"
} elseif { [ lindex $input 0 ] == 0 } {
	set in $input [ lindex 1 -1]
	if {[checkPrime $in]} {
		
	}
} else {
	puts "$input is a prime number"
}

Output:

Enter the number:
23
23 is a prime number

Enter the number:
21
21 is not a prime number