在应届生笔试中，经常会遇到进制的转换，可能会以不同的格式返回，下面的代码就是十进制转成二进制，分别以数组和字符串的形式返回，代码如下：

//10进制转成2进制，返回数组
-(NSMutableArray*)convertBinary:(int) decimal{
    
    NSMutableArray *tmp = [NSMutableArray arrayWithObjects:[NSNumber numberWithInt:0],[NSNumber numberWithInt:0],[NSNumber numberWithInt:0],[NSNumber numberWithInt:0],[NSNumber numberWithInt:0],[NSNumber numberWithInt:0],[NSNumber numberWithInt:0],[NSNumber numberWithInt:0],nil];
    NSUInteger index=7;
    int remainder =0;//余数
    int divisor = decimal;//整数
    while(divisor > 0) {
        remainder = divisor%2;
        [tmp replaceObjectAtIndex: index withObject:[NSNumber numberWithInt:remainder]];
        divisor=divisor/2;
        index--;
    }
    return tmp;
}

//十进制转二进制，返回字符串
- (NSString*)toBinarySystemWithDecimalSystem:(int)num length:(int)length
{
    int remainder =0;//余数
    int divisor =0;//除数
    NSString* prepare =@"";
    while(true)
    {
        remainder = num%2;
        divisor = num/2;
        num = divisor;
        prepare = [prepare stringByAppendingFormat:@"%d",remainder];
        if(divisor == 0){
            break;
        }
    }
    //倒序输出
    NSString* result = @"";
    for(int i = length -1; i >=0; i --){
        if(i <= prepare.length-1) {
            result = [result stringByAppendingFormat:@"%@",
                      [prepare substringWithRange:NSMakeRange(i ,1)]];
        }else{
            result = [result stringByAppendingString:@"0"];
        }
    }
    NSLog(@"result=%@",result);
    return result;
}