字节的不同单位间的转换

- (NSString *)fileSizeWithInterge:(NSInteger)size {
    // 1k = 1024, 1m = 1024k
    if (size < 1024) {// 小于1k
        return [NSString stringWithFormat:@"%ldB",(long)size];
    }else if (size < 1024 * 1024){// 小于1m
        CGFloat aFloat = size/1024;
        return [NSString stringWithFormat:@"%.0fKB",aFloat];
    }else if (size < 1024 * 1024 * 1024){// 小于1G
        CGFloat aFloat = size/(1024 * 1024);
        return [NSString stringWithFormat:@"%.1fM",aFloat];
    }else {
        CGFloat aFloat = size/(1024*1024*1024);
        return [NSString stringWithFormat:@"%.1fG",aFloat];
    }
}