C 语言中，没有修改数值，但数值自己变了？！

先发出来代码，大家可以跑跑看。

tp.h 文件：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef unsigned int Byte;

typedef struct {
  int sign; /* 0 for pos and 1 for neg */
  int size;
  Byte *tab;
} bignum;

#define BASE 10

#define MAX(a, b) (((a) > (b)) ? (a) : (b))
#define MIN(a, b) (((a) < (b)) ? (a) : (b))

void init(char *s, bignum *n) {
  int pos = 0;

  if (s[0] == '-') {
    n->sign = 1;
    n->size = strlen(s) - 1;
    // n->tab = calloc(n->size, sizeof(unsigned char));
    n->tab = (Byte *)malloc(n->size * sizeof(unsigned char));

    for (int i = n->size; i > 0; i--) {
      n->tab[pos] = s[i];
      pos++;
    }
  } else {
    n->sign = 0;
    n->size = strlen(s);
    // n->tab = calloc(n->size, sizeof(unsigned char));
    n->tab = (Byte *)malloc(n->size * sizeof(unsigned char));

    for (int i = n->size - 1; i >= 0; i--) {
      n->tab[pos] = s[i];
      pos++;
    }
  }
  // free(n->tab);
}

void showBigNum(bignum n) {
  if (n.sign == 1) {
    printf("-");
  }
  for (int i = n.size - 1; i >= 0; i--) {
    printf("%d", n.tab[i] - '0');
  }
}



tp.c 文件：
```C
#include "tp2.h"

int main(int argc, char *argv[]) {
  if (argc != 3) {
    printf("Please type 2 numbers as input\n");
    exit(1);
  }

  bignum a, b;

  init(argv[1], &a);
  /* You can try to comment the line below and start again, then you can see the difference */
  init(argv[2], &b);
  showBigNum(a);

  return 0;
}


可以试试：

**注释掉** 和 **不注释掉** *init(argv[2], &b);* 分别输出什么。

	gcc tp.c ; ./a.out 255555 122577

理论上都应该输出 255555.

求大佬帮助修改，并指出原因。

鱼和渔都想要，不要熊掌……