結論：
1. char 有符號範圍是-128~127；無符號範圍是0~255；
2. 在存儲媒介中，數字都是補碼形式儲存的（含字符常量）；
3. 正數補碼爲本身二進制，負數補碼：絕對值->取反->+1；
4. 補碼的補碼爲源碼：原碼求補碼是取反加1，補碼求原碼還是是取反加1（符號位除外） ！
例子：
root@ubuntu:/mnt/temp/test_8.31# gdb test<span style="white-space:pre"> </span><strong><span style="color:#ff0000;">//gdb調試</span></strong>
GNU gdb (Ubuntu 7.7.1-0ubuntu5~14.04.2) 7.7.1
Copyright (C) 2014 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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and "show warranty" for details.
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Reading symbols from test...done.
(gdb) list<span style="white-space:pre"> </span><strong><span style="color:#ff0000;">//源碼</span></strong>
1 #include <stdio.h>
2 #include <stdlib.h>
3
4 int main()
5 {
6 char a,b,c1,c2;
7 a = 197;
8 b = 198;
9
10 printf("%c,%c\n",a,b);
(gdb) list
11 printf("%d,%d\n",a,b);
12 exit(EXIT_SUCCESS);
13 }
(gdb) break 10<span style="white-space:pre"> </span><span style="color:#ff0000;"><strong>//斷點1爲第10行</strong></span>
Breakpoint 1 at 0x8048460: file test.c, line 10.
(gdb) break 11<span style="white-space:pre"> </span><strong><span style="color:#ff0000;">//斷點2爲第11行</span></strong>
Breakpoint 2 at 0x804847e: file test.c, line 11.
(gdb) r<span style="white-space:pre"> </span>//運行
Starting program: /mnt/temp/test_8.31/test
Breakpoint 1, main () at test.c:10
10 printf("%c,%c\n",a,b);
(gdb) cont<span style="white-space:pre"> </span><strong><span style="color:#ff0000;">//斷點1運行結果</span></strong><span style="white-space:pre"> </span>
Continuing.
�,
Breakpoint 2, main () at test.c:11
11 printf("%d,%d\n",a,b);
(gdb) cont<span style="white-space:pre"> </span><strong><span style="color:#ff0000;">//斷點2運行結果</span></strong>
Continuing.
-59,-58<span style="white-space:pre"> </span><span style="color:#ff0000;">//197 的補碼是11000101，最高位是1，所以是負數，剩1000101（補碼），求源碼爲111011，爲59，加符號位"1"，就是-59</span>
[Inferior 1 (process 19127) exited normally]