第一次使用qt，试着编译运行，qt自带的例子都可以运行了。
运行网上下载的一个程序时，出现以下错误怎么改啊？
src\main.cpp:18:24: mainwindow.h: No such file or directory
src\main.cpp: In function `int qMain(int, char**)':
src\main.cpp:28: error: `MainWindow' undeclared (first use this function)
src\main.cpp:28: error: (Each undeclared identifier is reported only once for ea
ch function it appears in.)
src\main.cpp:28: error: expected `;' before "mainWindow"
src\main.cpp:29: error: `mainWindow' undeclared (first use this function)
mingw32-make[1]: *** [debug\main.o] Error 1
mingw32-make[1]: Leaving directory `F:/pencil'
mingw32-make: *** [debug] Error 2
