The output of each function is piped to the next. The swap space is used instead. This does not put a complete ban on non-ANSI programs. Certain Turbo C features will work. Since character is machine specific, this serves to avoid confusion and common program errors when run on various platforms.
Different compilers have different defaults for the signedness of char.
Specifying whether a char should be signed or unsigned, removes ambiguity. For example, on the Windows compiler, this statement will be executed considering character as signed while on Linux they are executed considering character as unsigned. This shall result in dubious results because Windows will interpret the object differently. Output results to standard output file a.out. Compiles the file first.