Append variable to string

[Prodian]

Ok so Im trying to append a variable to the end of a string variable. Heres what Im doing but its not working:

string command = ("do this command now {0}",textbox1.text);

what Im really trying to do is set a command in telnet for a router command to append an textbox.text to whatever the user input in the text box. it send it fine with just the command stored into the string but not when I try to add the textbox.text to the end and try to store it all into a string. any suggestions? or does this even make sense? thanks.

[int08h]

Try

string command = string.Format("do this command now {0}",textbox1.text);

[sindia]

try this

string command = "do this command now " + textbox1.text;