If you are using Turbo C in Windows 7 or Vista it will not allowed full-screen mode because turbo c is developed in 16 bit and vista and 7 not support it .
1.)Open TC++ (normally C:\TC\BIN\TC.EXE).In the startup it will show a dialogue box that it doesn’t support full screen mode as seen in the picture below. Just select ignore option.
3.)Now it will show the properties window, in which you select the Font tab. There you can see two font options as Raster and Lucida Console. The default will be Raster. You select Lucida Console and select the size from the size list as 28.