system normally waits for the child process to finish, but there are exceptions.

• If you do system "... &" on unix, system will return without waiting for the child process to finish.
• If you do system -1, ... on Windows, system will return without waiting for the child process to finish.
• Some application launch another application and exit immediately (like the Windows command start), so system would return immediately too.
• Running a windowed (as opposed to console) application in Windows will also cause system to return immediately (IIRC).