dont display what i have typed

[sacin]

i want to make a program which displays some other letter if something is typed.
for example:
in the output screen if someone types:"a"
i want some other letter:"y"

simply speaking i want to trick others to think that their keyboard is spoilt;
but there is a problem, when i type something in the output screen it is displayed even though i dont desire it to be displayed in the cin>> operation.