checking the value of the variable

Shell Programming and Scripting
1

Does anyone know the quick way to check if the variable contains only numeric characters, for example:
A=123445 - correct
B=#f123* - incorrect
I am in ksh88i Thanks a lot for help -A

2

For integers:

case $var in 
  "" | *[!0-9]* ) echo invalid number ;;
              * ) echo OK ;;
esac