Please, how can I write a C program that will check inverting two characters instead of doing if and-CodePudding

If the user enters one the passwords below, I will ask him about secret question, but I don't do it using if else...

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

#define SIZE 20

int main(void) {
    char pass[SIZE];
    char originalPass[SIZE] = "abcDEF123=!)";
    printf("Password: ");
    fgets(pass, sizeof pass, stdin);
    printf("\n");
                      
    // if the user enters one the passwords bellow, I will ask him about secret Q
    // but I don't do it using if else...

    /* 
      bacDEF123=!)
      acbDEF123=!)
      abDcEF123=!)
      abcEDF123=!)
      abcDFE123=!)
      abcDE1F23=!)
      abcDEF213=!)
      abcDEF132=!)
      abcDEF12=3!)
      abcDEF123!=)
      abcDEF123=)!
    */
    return 0; 
}

CodePudding user response：

You could enter all the passwords into an array and use a for (or any other loop) loop to iterate through the array and compare each element to the originalPass.

EDIT: Please dont use gets, use fgets instead

#define LENGTH   //number of strings 
char passwords[LENGTH][SIZE]= { //enter strings here }; 
int i =0; 
while(i<LENGTH)
{ 
  if( strcmp(passwords[i], originalPass) == 0) 
    { 
       // do something
    }
  i  ; 
}

CodePudding user response：

You can use a fuzzy comparison function:

/* return 0 if the strings compare equal,
          1 if they compare equal with a single swap
          -1 otherwise
*/
int fullycmp(const char *s1, const char *s2) {
    int swap = 0;
    size_t i = 0;
    size_t len1 = strlen(s1);
    size_t len2 = strlen(s2);

    if (len1 != len2)
        return -1;

    while (i < len && s1[i] == s2[i])
        i  ;

    if (i < len - 1 && s1[i] == s2[i   1] && s1[i   1] == s2[i]) {
        swap = 1;
        i  = 2;
    }
    while (i < len && s1[i] == s2[i])
        i  ;

    return i == len ? swap : -1;
}

If you really must not use if or else, you can replace the if statements above with while statements:

int fullycmp(const char *s1, const char *s2) {
    int swap = 0;
    size_t i = 0;
    size_t len1 = strlen(s1);
    size_t len2 = strlen(s2);

    while (len1 != len2)
        return -1;

    while (i < len && s1[i] == s2[i])
        i  ;

    while (i < len - 1 && s1[i] == s2[i   1] && s1[i   1] == s2[i]) {
        swap = 1;
        i  = 2;
        break;
    }
    while (i < len && s1[i] == s2[i])
        i  ;

    return i == len ? swap : -1;
}

Also make sure you strip the newline with:

pass[strcspn(pass, "\n")] = '\0'; // strip the trailing newline