转换说明符(%s、%u、%c.....)

printf("%x %X %#x",31,31,31);
//1f 1F 0x1f

NSString *aa = [NSString stringWithFormat:@"%10d",100];
//       100  右移10个字符位置宽
NSString *aaa = [NSString stringWithFormat:@"%-10d",100];
//100         左移10个字符位置宽

const char *cc = "A good girl tell me that.....I V U";
printf("%.11s\n%35s\n%36s\n%37s\n%-37s",cc,cc,cc,cc,cc);
/*
A good girl
A good girl tell me that.....I V U
A good girl tell me that.....I V U
A good girl tell me that.....I V U
A good girl tell me that.....I V U   (lldb)
*/