simple loop error in objC

Hello I have a loop and开发者_开发问答 I have issues when int11=21 and when i=7.

-(NSString *)print01:(int)int11{
    int n =128;
    char array12[7];
    NSString *str;

if(int11==0)
 return str= [NSString stringWithFormat:@"00000000"];


    for(int j=0;j<8;j++)
        if ((int11-n)>=0){
             //When i=7 then int11=1 and n=1, the "i" here is 7
                      array12[j]='1'; 
              //and here is become 49!!!

            int11-=n;

        }
        else 
            array12[j]='0';

        n=n/2;
        NSLog(@"Last %d",j);
    }


   str= [NSString stringWithFormat:@"%s",array12];

    return str;
}

char array12[7]; and for(int j=0;j<8;j++) and array12[j]='1'; induce an out-of-bounds problem.