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賦值爲-1， 與宏NUM-2（值爲5）相比較，這時d轉化爲無符號的數，所以條件爲假，for循環未進入，若將NUM換爲 const int就不會出現這樣的狀況。

延伸：在有符號和無符號的數比較時，有符號的數將先轉化成無符號的數而後再比較。有一篇博文寫的比較詳細：
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;
}

。。。。。。居然只是變量名錯了，OS_HP-UX_print  變量名中含-

 

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;  }

輸出結果是：hello-errhello-out，stdout, stder分別表示標準輸出，標準錯誤，默認都是將信息輸出到終端上，在默認狀況下，stdout是行緩衝的，他的輸出會放在一個buffer裏面，只有到換行的時候，纔會輸出到屏幕。而stderr是無緩衝的，會直接輸 出，舉例來講就是fprintf(stdout, "xxxx") 和 fprintf(stdout, "xxxx\n")，前者會憋住，直到遇到新行纔會 一塊兒輸出。而fprintf(stderr, "xxxxx")，無論有麼有\n，都輸出。