If you start TCC from another program (e.g. to run a batch file or internal command), it will return a numeric code to the other program when it exits. This code indicates whether or not the operation performed was successful, with 0 indicating success and a non-zero value indicating a failure or other numeric result.
TCC's exit code is normally the numeric exit code from the last internal or external command. However, for CMD compatibility reasons and to avoid conflicts with external commands, only some internal commands set the exit code; others leave it unchanged from the most recent external command.