outFile.write((char *) &ac, sizeof(account));

[mohamed atteya]

i wanna know the general function used in this line: " outFile.write((char *) &ac, sizeof(account)); " and what exactly does it do?

[Peter87]

You mean the write function? If outFile is a std::ofstream, then the first argument is a pointer (char*) to the data and the second argument is the number of bytes to be written to the file.