小编Pha*_*est的帖子

I have a list of tuples as shown:

lt = [(1,'a'),(1,'b'),(2,'a'),(3,'b'),(3,'c')]

I want to make the numbers keys of a dictionary and have them point to a list. That list then holds all associations in the list of tuples. So in the list above, it would split into a dictionary as:

dict_lt:{
1:[a,b],
2:[a],
3:[b,c]
}

Currently I use the dictionary's flexibility in automatically declaring new keys, which I then force point to an empty list. Then I fill that …

#include <stdio.h>
#define PREC 4

int main()
{
    long l = 12;
    printf("%PRECld", l);
}

我将如何使用它PREC来定义所需的精度？即预期的产出是0012。目前正在印刷%PRECld。