C-为什么无法正常运行？ 我是C新手

Question

The following code is running, but when I enter the username and the correct password it is always printing " The username doesn't exist. Try again with another username please. " Why?

#include <stdio.h>
#include <string.h>
#define MAX_PASSWORD_LENGTH 10
#define MAX_USERNAME_LENGTH 10
#define MAX_USERS 15

int main(void) {

  char usernames[MAX_USERS][MAX_USERNAME_LENGTH + 1] = { "nnikolaou", "stakis",
      "sanitsaki" };

  char passwords[MAX_USERS][MAX_PASSWORD_LENGTH + 1] = { "n32", "s4343",
      "s5343" };

  char user_access_rights[MAX_USERS] = { 'r', 'a', 's' };

  int i;
  char username_entered[MAX_USERNAME_LENGTH + 1];

  char password_entered[MAX_PASSWORD_LENGTH + 1];

  float ret1;

  int abc;

  int username_position;

  abc = 0;

  printf("Enter username please, with a maximum length of %ld characters:",
      MAX_USERNAME_LENGTH);

  for (i = 0; i < MAX_USERNAME_LENGTH; i++) {
    username_entered[i] = getchar();
    if (username_entered[i] == '\n') {
      break;
    }
  }
  printf("Enter password please, with a maximum length of %ld characters:",
      MAX_PASSWORD_LENGTH);
  for (i = 0; i < MAX_PASSWORD_LENGTH; i++) {

    password_entered[i] = getch();
    if (password_entered[i] == '\r') {
      break;
    }

    putchar('*');
  }

  for (i = 0; i < MAX_USERS; i++) {
    ret1 = strcmp(username_entered, usernames[i]);

    if (ret1 == 0) {
      username_position = i;
      abc = 1;
      printf("\n");
      printf("The username has been found.");
    } else {
      if (i == MAX_USERS + 1) {
        abc = 0;
      }
    }
  }

  if (abc == 0) {
    printf("\n");
    printf(
        "The username doesn't exist. Try again with another username please.");
    printf("\n");
    return 1;
  }

  return 0;
}

I believe that it is problem of strcmp . It should be written in this way, using strcmp.

Answer 1

I see couple of problems.

1. You are including the '\\n' in the name when accepting user input.
2. You are not terminating the name with a null character.

Tweak your code a little bit to fix those.

for(i=0; i<MAX_USERNAME_LENGTH; /* i++ Increment i only in one branch */){
   int c = getchar();
   if ( c == '\r' )
   {
      // Ignore it.
      // Don't increment i for this.
   }
   else if ( c == '\n')
   {
      break;
   }
   else
   {
      // Store the character and increment i.
      username_entered[i] = c;
      i++;
   }
}
username_entered[i] = '\0';