C编译器认为char类型是int类型-Clang编译器

Question

So I am going through one of those edX courses in computer science (not for credit, just to have lectures to help self-learning) and the advanced problem set has to do with decrypting passwords. To get a better understanding of the function crypt() used to make the encryptions, I made the following code to figure out what was being used for the "salts" string (the man crypt() command in the terminal said: ("salt is a two-character string chosen from the set [a-zA-Z0-9./]. This string is used to perturb the algorithm in one of 4096 different ways.")) Please tell me if you can see why I am getting this error.

Below is the code I used. I am getting this error when attempting to compile:

test.c:37:33: error: incompatible integer to pointer conversion passing 'char' to
parameter of type 'char *'; take the address with & [-Werror,-Wint-conversion]
char *salt = strcat(whatever1,whatever2);

Code:

    #define _XOPEN_SOURCE //this is needed for the unistd and crypt stuff
    #include <stdio.h>
    #include <unistd.h> //this lets me do the crypt() fcn
    #include <cs50.h> //just lets me use string as a type among w/some input fcns and       is made by the course
    #include <string.h>
    #include <ctype.h> //this lets me use toascii()

    char *word = "caesar";
    char *password;

    char toASCII_New(int i) //attempt to turn input to HEX then corresponding ASCII character
    {
        for(int num = i; num<= 172; num++)
        {
            for(int hex_num = 0x41; hex_num <= 0x7a; hex_num++)
            {
                if(num == hex_num)
                {
                    char letter = (char) toascii(hex_num); //should convert hex to ascii here
                    return letter;
                }
            }
        }
        char backup = 'a';
        return backup;
    }


    string checker(int first, int second) //Checks the inputs to see if the can be the correct SALTS input to crypt
    {
        for (int i = first; i<=first+25; i++)
        {
            for(int j = second; j<=second+25; j++)
            {
                char whatever1 = (char) toASCII_New(i);
                char whatever2 = (char) toASCII_New(j);
                char *salt = strcat(whatever1,whatever2);
                password = crypt(word,salt);
                int compare = strcmp(password,"50zPJlUFIYY0o"); // this is what i'm really checking
                if (compare == 0)
                    return salt;

            }
        }
    return "no";
    }


    int main(void)
    {
        string AA = checker(65,65);
        string Aa = checker(65,97);
        string aA = checker(97,65);
        string aa = checker(97,97);

        printf("AA: %s\nAa: %s\naA: %s\naa: %s\n",AA,Aa,aA,aa);
    }

Answer 1

strcat is for concatenating strings not 2 separate chars. "whatever1" will hold the joined string together. Why using -dangerous- strcat operations when all you have to do is to have a 2-byte string ? Just use something like:

char salt[3];
salt[0]=toASCII_New(i); /* why the casting to char ? you already returned a char... */
salt[1]=toASCII_New(j);
salt[2]='\0'; /* to terminate the string properly */

Answer 2

Here are some general advices, as the entire code needs to be refactored:

---

Function toASCII_New should be rewritten as follows:

char toASCII_New(int c)
{
    if (('A' <= c && c <= 'Z') || ('a' <= c && c <= 'z'))
        return (char)toascii(c);
    return 'a';
}

---

Function checker should be rewritten as follows:

int checker(int first, int second, char salt[3])
{
    for (int i=first; i<=first+25; i++)
    {
        for (int j=second; j<=second+25; j++)
        {
            salt[0] = toASCII_New(i);
            salt[1] = toASCII_New(j);
            password = crypt(word,salt);
            if (strcmp(password,"50zPJlUFIYY0o") == 0)
                return 1;
        }
    }
    return 0;
}

---

Function main should be rewritten as follows:

int main()
{
    char salt_AA[3] = {0};
    char salt_Aa[3] = {0};
    char salt_aA[3] = {0};
    char salt_aa[3] = {0};
    int  salt_AA_OK = checker('A','A');
    int  salt_Aa_OK = checker('A','a');
    int  salt_aA_OK = checker('a','A');
    int  salt_aa_OK = checker('a','a');
    printf("AA: %s\n",salt_AA_OK? salt_AA:"failed");
    printf("Aa: %s\n",salt_Aa_OK? salt_Aa:"failed");
    printf("aA: %s\n",salt_aA_OK? salt_aA:"failed");
    printf("aa: %s\n",salt_aa_OK? salt_aa:"failed");
    return 0;
}