按键没有按下去,j没有变，为什么点阵上的图案会变

Question

#include<reg51.h>
unsigned char j=0;
unsigned char i=0;
void delay(unsigned int i)
{
unsigned char t;
while(i--)
{
for(t=0;t<120;t++);
}
}
sbit key7=P1^7;
unsigned char string[]={
0x80,0x00,0x80,0x00,0x80,0x00,0xFC,0x1F,0x84,0x10,0x84,0x10,0x84,0x10,0xFC,0x1F,
0x84,0x10,0x84,0x10,0x84,0x10,0xFC,0x1F,0x84,0x50,0x80,0x40,0x80,0x40,0x00,0x7F,

0x08,0x00,0x08,0x00,0xFC,0x3F,0x04,0x00,0xF2,0x0F,0x01,0x00,0xFC,0x0F,0x00,0x08,
0x00,0x08,0x00,0x08,0x00,0x08,0x00,0x08,0x00,0x50,0x00,0x50,0x00,0x60,0x00,0x40,

0x10,0x00,0xF8,0x07,0x04,0x04,0xFE,0x1F,0x85,0x10,0x44,0x10,0xFC,0x1F,0x60,0x00,
0x98,0x08,0x46,0x05,0x30,0x03,0x8E,0x05,0x60,0x09,0x18,0x11,0x47,0x61,0x80,0x00,
};
void key()
{
    if(key7==0)
    {
    delay(200);
    if(key7==0)
    j++;
    while(key7==0);
    }
    if(j==3)
    j=0;
}
void matrix()
{
            for(i=0;i<16;i++)
            {
            P1=i;
            P0=string[j*32+i*2];
            P2=string[j*32+i*2+1];
            delay(1);
            }
}
void main()
{
while(1)
{
key();
matrix();
}
}