How do I set the value of a environment variable to a variable?

I am running a script in which a user enters a command and I need to take that input and assign it to an environment variable, ex. PWD=string. Can it be done using putenv or is there another function to do it?

Have you tried using the equals (=) operator?

export PWD=$input
-- or --
PWD=$input; export PWD
-- or (for csh) --
setenv PWD $input

yes i have tried them and I am still having trouble getting the value of the string into the variable. For putenv I need to do something like putenv("PWD=string") but then I am getting PWD literally equal to "string". I need a way to get the value of string into PWD

Which OS and shell are you using?