1 #include <stdio.h>
 2
 3 int main()
 4 {
 5     unsigned short a = 1;
 6     unsigned short b = 0;
 7
 8     if (a < (b-1)) //a和b-1的结果-1都被转换为int类型进行比较，1<-1，显然false
 9     {
10         printf("in if\n");
11     }
12
13     return 0;
14
15 }  

 1 #include <stdio.h>
 2
 3 int main()
 4 {
 5     unsigned short a = 1;
 6     unsigned int b = 0;
 7
 8     if (a < (b-1)) //b-1的结果-1，被转换为0xffffffff，1<0xffffffff，显然true啊
 9     {
10         printf("in if\n");
11     }
12
13     return 0;
14
15 }  

 1 08048425 <main>:
 2  8048425:      8d 4c 24 04              lea    0x4(%esp),%ecx
 3  8048429:      83 e4 f0                 and    $0xfffffff0,%esp
 4  804842c:      ff 71 fc                 pushl  -0x4(%ecx)
 5  804842f:      55                       push   %ebp
 6  8048430:      89 e5                    mov    %esp,%ebp
 7  8048432:      51                       push   %ecx
 8  8048433:      83 ec 14                 sub    $0x14,%esp
 9  8048436:      66 c7 45 f6 01 00        movw   $0x1,-0xa(%ebp)
10  804843c:      66 c7 45 f4 00 00        movw   $0x0,-0xc(%ebp)
11  8048442:      0f b7 45 f6              movzwl -0xa(%ebp),%eax
12  8048446:      0f b7 55 f4              movzwl -0xc(%ebp),%edx
13  804844a:      83 ea 01                 sub    $0x1,%edx
14  804844d:      39 d0                    cmp    %edx,%eax
15  804844f:      7d 10                    jge    8048461 <main+0x3c>
16  8048451:      83 ec 0c                 sub    $0xc,%esp
17  8048454:      68 00 85 04 08           push   $0x8048500
18  8048459:      e8 a2 fe ff ff           call   8048300 <puts@plt>
19  804845e:      83 c4 10                 add    $0x10,%esp
20  8048461:      b8 00 00 00 00           mov    $0x0,%eax
21  8048466:      8b 4d fc                 mov    -0x4(%ebp),%ecx
22  8048469:      c9                       leave
23  804846a:      8d 61 fc                 lea    -0x4(%ecx),%esp
24  804846d:      c3                       ret
25  804846e:      66 90                    xchg   %ax,%ax