do - while循环,具有c中的多个条件

Question

我试图做一个while-do循环退出当用户键入exit或退出时.由于某种原因,我无法理解我简单无法实现它.如果我单独应用其中一个条件它可以正常工作,但我需要同时具备这两个条件.

我在网上搜索,我发现了几个不同编程语言的例子,例如(PHP)Do-While循环多条件,(Python)如何进行while循环多条件,(C++)在do ... while循环中使用多个条件等但无论我遵循什么程序,我都能同时兼顾两种情况.

理想的解决方案是添加大写条件,但我可以在解决此问题后立即使用它.

也许一双新鲜的眼睛会看到我失踪的东西.

代码示例如下:

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

#define MAX_CHARACTERS 250
#define MAX_USERNAME 12
#define MAX_USERS 1024
#define MIN_REQUIRED 3
#define MAX_PORT 65536
#define MIN_PORT 1

typedef struct rec {
  char username[MAX_USERNAME];
  char msg[MAX_CHARACTERS];
}RECORD;

/* Usage Instructions void because we do not have any return */
int help(void) {
  printf("Usage: test.c [-s <arg0>] [-s <arg1>]\n");
  printf("\t-s: a string program name <arg0>\n");
  printf("\t-s: a string with a Nickname maximum characters %i <arg2>\n",MAX_USERNAME);
  return (1);
}

int main(int argc, char **argv) {

  if ( argc < MIN_REQUIRED ) {
    printf ("Please follow the instructions: not less than %i argument inputs\n",MIN_REQUIRED);
    return help();
  }
  else if ( argc > MIN_REQUIRED ) {
    printf ("Please follow the instructions: not more than %i argument inputs\n",MIN_REQUIRED);
    return help();
  }
  else {

    RECORD *ptr_record;

    ptr_record = (RECORD *) malloc (sizeof(RECORD));

    if (ptr_record == NULL) {
      printf("Out of memmory!\nExit!\n");
      exit(0);
    }

    char username_argv[MAX_USERNAME];

    memset( username_argv , '\0' , sizeof(username_argv) );

    if (strlen(argv[2]) > 12 ) {
      printf("Maximum characters for Nickname: %i\nPlease try again!\n",MAX_USERNAME);
      exit(0);
    }

    strcpy( username_argv , argv[1] );

    strncpy( (*ptr_record).username , username_argv , sizeof(username_argv) );

    printf("Username pointer: %s\n",(*ptr_record).username);

    do {
      printf("Please enter your MSG:\n");
      scanf ("%s",(*ptr_record).msg);
      printf("User MSG: %s\n",(*ptr_record).msg);
      //} while ((strcmp((*ptr_record).msg,"exit") != 0) || (strcmp((*ptr_record).msg,"quit") != 0));
      //} while (strcmp((*ptr_record).msg,"exit") || strcmp((*ptr_record).msg,"quit") != 0);
      //} while ((strcmp((*ptr_record).msg,"exit")) || (strcmp((*ptr_record).msg,"quit")) != 0);
      //} while ((*ptr_record).msg != "quit" || (*ptr_record).msg != "exit");
    } while (((*ptr_record).msg != exit) || ((*ptr_record).msg != ));

    free(ptr_record);

    return 0;
  } /* End of else */
} /* End of main() */"

Answer 1

你试过了吗:

} while ((strcmp((*ptr_record).msg,"exit") != 0) &&   
(strcmp((*ptr_record).msg,"quit") != 0));

你想要的NOT (A OR B)不是NOT A OR NOT B.请记住De Morgan的法律,即与之NOT (A OR B)相同NOT A AND NOT B.

使用||是错误的,因为您将始终至少有一个条件(操作数||)或另一个条件为真.

想象一下你的字符串是"exit":

(strcmp((*ptr_record).msg,"exit") != 0)

是假的

但

(strcmp((*ptr_record).msg,"quit") != 0)

是真的.

这意味着0 || 1哪个收益率 1."quit"字符串相同(相反)(1 || 0产生1).对于其他字符串,两个操作数都||将是1和1 || 1yield 1.