#include <reg51.h>
void delays(unsigned int i);
void main(void)
{
    char LED;
    LED = 0xfe;
    unsigned char i;
    unsigned char j;
    while(1)
    {
        for (i = 255; i > 0; i--)
        {
            P2 = LED;                     
            delays(500);
            LED = LED << 1;
            LED = LED | 0x01;
            if (LED == 0x7f)
                break;
        }
        for (j = 255; j > 0; j--)
        {
            P2 = LED;
            delays(500);
            LED = LED >> 1;
            LED = LED | 0x80;

        }
    }
}

void delays(unsigned int i)
{
    unsigned char j;
    for (i; i > 0; i--)
        for (j = 255; j > 0; j--) ;
}


返回
DEMO.C(7): error C141: syntax error near 'unsigned'
DEMO.C(7): error C202: 'i': undefined identifier
DEMO.C(8): error C141: syntax error near 'unsigned'
DEMO.C(8): error C202: 'j': undefined identifier
DEMO.C(11): error C202: 'i': undefined identifier
DEMO.C(19): error C202: 'j': undefined identifier
Target not created

谢谢了，我想在咨询一个问题
请看：
#include "iostream.h"

void main()
{
    int x;
    x = 1;
    int y;
}

return ：

--------------------Configuration: C_1 - Win32 Debug--------------------
Compiling...
C_1.CPP
C:\Documents and Settings\Administrator\桌面\app_soft\2013\C_program_keti\test\C_1.CPP(7) : warning C4101: 'y' : unreferenced local variable

C_1.OBJ - 0 error(s), 1 warning(s)

编译器是VSC++6.0   
是不是说 C语言要求全部变量在程序的开头进行定义，这个规则是根据编译器的不同而不同。