字符串反转时链接出现问题，求助大侠
程序代码：char *revstr(char *str,size_t len)
{
char *start=str;
char *end=str+len-1;
char ch;
if (start<end)
{
ch=*start;
*start=*end;
*end=ch;
start++;
end--;
}
return str;
}编译没有问题，链接出现问题如下：
--------------------Configuration: reversal - Win32 Debug--------------------
Linking...
LIBCD.lib(crt0.obj) : error LNK2001: unresolved external symbol _main
Debug/reversal.exe : fatal error LNK1120: 1 unresolved externals
Error executing link.exe.
reversal.exe - 2 error(s), 0 warning(s)
Linking...
LIBCD.lib(crt0.obj) : error LNK2001: unresolved external symbol _main
Debug/reversal.exe : fatal error LNK1120: 1 unresolved externals
Error executing link.exe.
reversal.exe - 2 error(s), 0 warning(s)
