Intersting C examples

From C Puzzles

The expected output of the following C program is to print the elements in the array. But when actually run, it doesn't do so.

#include<stdio.h>   #define TOTAL_ELEMENTS (sizeof(array) / sizeof(array[0]))   int array[] = {23,34,12,17,204,99,16};   int main()   {       int d;       for(d=-1;d <= (TOTAL_ELEMENTS-2);d++)           printf("%d\n",array[d+1]);       return 0;   }

d赋值为-1， 与宏NUM-2（值为5）相比较，这时d转化为无符号的数，因此条件为假，for循环未进入，若将NUM换为 const int就不会出现这样的情况。

延伸：在有符号和无符号的数比较时，有符号的数将先转化成无符号的数然后再比较。有一篇博文写的比较详细：
http://www.360doc.com/content/14/0320/17/1317564_362209181.shtml

I thought the following program was a perfect C program. But on compiling, I found a silly mistake. Can you find it out (without compiling the program :-) ?

#include<stdio.h>
void OS_Solaris_print()
{        printf("Solaris - Sun Microsystems\n");
}
void OS_Windows_print()
{        printf("Windows - Microsoft\n");

}
void OS_HP-UX_print()
{        printf("HP-UX - Hewlett Packard\n");
}
int main()
{        int num;       
         printf("Enter the number (1-3):\n");        
         scanf("%d",&num);        
         switch(num)
        {               
         case 1:                     
            OS_Solaris_print();                     
            break;              
         case 2:                     
             OS_Windows_print();                    
             break;               
         case 3:                    
             OS_HP-UX_print();             
             break;             
        default:           
             printf("Hmm! only 1-3 :-)\n");  
             break;
        }       
        return 0;
}

。。。。。。竟然只是变量名错了，OS_HP-UX_print  变量名中含-

The following program doesn't "seem" to print "hello-out". (Try executing it)

#include <stdio.h>   #include <unistd.h>   int main()  {          while(1)          {                  fprintf(stdout,"hello-out");                  fprintf(stderr,"hello-err");                  sleep(1);          }          return 0;  }

输出结果是：hello-errhello-out，stdout, stder分别表示标准输出，标准错误，默认都是将信息输出到终端上，在默认情况下，stdout是行缓冲的，他的输出会放在一个buffer里面，只有到换行的时候，才会输出到屏幕。而stderr是无缓冲的，会直接输 出，举例来说就是printf(stdout, "xxxx") 和 printf(stdout, "xxxx\n")，前者会憋住，直到遇到新行才会 一起输出。而printf(stderr, "xxxxx")，不管有么有\n，都输出。