Is there any possible way to loop strcmp function in c language? - c

Question

I'm a freshman in university and currently learning the C language. Last night I've just found really big problem with my code but there's nothing I could fix with my terrible skills... can you help me to solve this?
(condition)
you are trying to login with id / pw and only have 3 chances.
there are 5 id's and pw's on each.
if id does not exist, print id does not exist.
if id exists but pw does not match, print pw does not match.
if id and pw match, print login successful and exit program.
is there any way to loop the strcmp functions which marked?
Here's code below.
#include <stdio.h>
#include <string.h>
int main(void) {
char id0[] = "user1";
char id1[] = "user2";
char id2[] = "user3";
char id3[] = "user4";
char id4[] = "user5";
char pw0[] = "pass1";
char pw1[] = "pass2";
char pw2[] = "pass3";
char pw3[] = "pass4";
char pw4[] = "pass5";
char idsol[100] = { 0 };
char pwsol[100] = { 0 };
int idmat = 1;
int pwmat = 1;
int logstack = 0;
for (int i = 0; i <= 2;) {
logstack = i;
rewind(stdin);
printf("ID: ");
scanf_s("%s", idsol, sizeof(idsol));
printf("PW: ");
scanf_s("%s", pwsol, sizeof(pwsol));
if (strcmp(idsol, id0) == 0) { //i want to make these 5 blocks in one command.
idmat = 0;
if (strcmp(pwsol, pw0) == 0) {
pwmat = 0;
}
}
if (strcmp(idsol, id1) == 0) {
idmat = 0;
if (strcmp(pwsol, pw1) == 0) {
pwmat = 0;
}
}
if (strcmp(idsol, id2) == 0) {
idmat = 0;
if (strcmp(pwsol, pw2) == 0) {
pwmat = 0;
}
}
if (strcmp(idsol, id3) == 0) {
idmat = 0;
if (strcmp(pwsol, pw3) == 0) {
pwmat = 0;
}
}
if (strcmp(idsol, id4) == 0) { //these 5 blocks!!!
idmat = 0;
if (strcmp(pwsol, pw4) == 0) {
pwmat = 0;
}
}
if (idmat != 0) {
printf("ID does not exist.\n");
i++;
idmat = 1;
}
else if (idmat == 0 && pwmat != 0) {
printf("PW does not match.\n");
i++;
idmat = 1;
} else {
logstack = 0;
break;
}
}
if (logstack >= 2) {
printf("login failed.\n");
} else {
printf("login successful!\n");
}
return 0;
}
Thanks for any comment! have a nice day

Answer 1

You should use arrays to gather the values to be used in loops.
#include <stdio.h>
#include <string.h>
int main(void) {
char id0[] = "user1";
char id1[] = "user2";
char id2[] = "user3";
char id3[] = "user4";
char id4[] = "user5";
char pw0[] = "pass1";
char pw1[] = "pass2";
char pw2[] = "pass3";
char pw3[] = "pass4";
char pw4[] = "pass5";
/* gather strings in arrays */
char* ids[] = { id0, id1, id2, id3, id4 };
char* pws[] = { pw0, pw1, pw2, pw3, pw4 };
char idsol[100] = { 0 };
char pwsol[100] = { 0 };
int idmat = 1;
int pwmat = 1;
int logstack = 0;
for (int i = 0; i <= 2;) {
logstack = i;
rewind(stdin);
printf("ID: ");
scanf_s("%s", idsol, sizeof(idsol));
printf("PW: ");
scanf_s("%s", pwsol, sizeof(pwsol));
/* use the arrays for looping */
for (int j = 0; j < 5; j++) {
if (strcmp(idsol, ids[j]) == 0) {
idmat = 0;
if (strcmp(pwsol, pws[j]) == 0) {
pwmat = 0;
}
}
}
if (idmat != 0) {
printf("ID does not exist.\n");
i++;
idmat = 1;
}
else if (idmat == 0 && pwmat != 0) {
printf("PW does not match.\n");
i++;
idmat = 1;
}
else { logstack = 0; break; }
}
if (logstack >= 2) {
printf("login failed.\n");
}
else { printf("login successful!\n"); }
return 0;
}
Another way is putting the string directly in arrays:
#include <stdio.h>
#include <string.h>
int main(void) {
char ids[][6] = {
"user1",
"user2",
"user3",
"user4",
"user5"
};
char pws[][6] = {
"pass1",
"pass2",
"pass3",
"pass4",
"pass5"
};
char idsol[100] = { 0 };
char pwsol[100] = { 0 };
/* omit: same as the first code */
}

Answer 2

I have just defined a function to do the looping and changed your array definitions into a list of strings. The code is below (follow the explanations in the code):
#include <stdio.h>
#include <string.h>
#define NTIMES 3 /* ask three times for a password */
/* this table organization allows you to iterate for each pair of ids[i]
* and pws[i]. */
char *ids[] = {
"user1",
"user2",
"user3",
"user4",
"user5",
NULL, /* to indicate we are finished this controls how the end of
* the list is reached below */
};
char *pws[] = {
"pass1",
"pass2",
"pass3",
"pass4",
"pass5", /* don't need to add a NULL here, but there
* must be as many entries as for used ids */
};
/* this function searches the two tables above for a valid user/pass match */
int check_user(char *user, char *pass)
{
int id;
for (id = 0; ids[id] != NULL; id++) { /* iterate the list */
if (0 == strcmp(ids[id], user)) { /* if user found */
if (0 == strcmp(pws[id], pass)) { /* if pass matches */
printf("Found user %d, id=%s\n", id, ids[id]);
return id; /* found user, return value of id to know
* outside which user was selected. */
} else {
printf("PW does not match\n");
/* we continue for the next pair in the loop */
}
}
}
/* we ended the loop without a valid user/pass match */
printf("ID %s does not exist, or password incorrect\n", user);
return -1; /* not found, we return a number out of the valid range */
}
int main(void) {
/* initializing these variables is not neccessary as you assign them
* (by reading into them from stdin) before using. But it is a good
* practice, so it is more difficult that you forget initializing
* variables that should have a default value. */
char idsol[100] = { 0 };
char pwsol[100] = { 0 };
// int idmat = 1; // unnecessary
// int pwmat = 1; // unnecessary
// int logstack = 0; // unnecessary
/* we need to declare times outside the for loop, because we are using
* the last value assigned to it in the loop, so in case we get out of
* the loop prematurely, we know we got a valid user. */
int times = -1; /* we initialize, for the same reason explained above */
for (times = 0; times < NTIMES; times++) {
// logstack = i; // unnecessary
// rewind(stdin); // unnecessary
printf("ID: ");
if (!fgets(idsol, sizeof idsol, stdin)) {
break; /* EOF on input, get out of the loop */
}
char *id_pointer = strtok(idsol, "\n"); /* take off the last
* newline */
// scanf_s("%s", idsol, sizeof(idsol)); // scanf_s is not standard
printf("PW: ");
if (!fgets(pwsol, sizeof pwsol, stdin)) {
break; /* EOF while reading input, get out of the loop */
}
char *pass_pointer = strtok(pwsol, "\n"); /* take off the newline */
// scanf_s("%s", pwsol, sizeof(pwsol)); // scanf_s is not standard
/* this calls the function above that tests a username/password
* and prints the messages in the block below */
if (check_user(id_pointer, pass_pointer) >= 0)
break; /* get out of the loop */
/* this was the code you wanted to eliminate, so here it is, commented */
// if (strcmp(idsol, id0) == 0) { //i want to make these 5 blocks in
// one command.
// idmat = 0;
// if (strcmp(pwsol, pw0) == 0) {
// pwmat = 0;
// }
// }
// if (strcmp(idsol, id1) == 0) {
// idmat = 0;
// if (strcmp(pwsol, pw1) == 0) {
// pwmat = 0;
// }
// }
// if (strcmp(idsol, id2) == 0) {
// idmat = 0;
// if (strcmp(pwsol, pw2) == 0) {
// pwmat = 0;
// }
// }
// if (strcmp(idsol, id3) == 0) {
// idmat = 0;
// if (strcmp(pwsol, pw3) == 0) {
// pwmat = 0;
// }
// }
// if (strcmp(idsol, id4) == 0) { //these 5 blocks!!!
// idmat = 0;
// if (strcmp(pwsol, pw4) == 0) {
// pwmat = 0;
// }
// }
// if (idmat != 0) {
// printf("ID does not exist.\n");
// i++;
// idmat = 1;
// }
// else if (idmat == 0 && pwmat != 0) {
// printf("PW does not match.\n");
// i++;
// idmat = 1;
// } else {
// logstack = 0;
// break;
// }
}
/* i have changed slightly this code also to use a single constant
* (by using its name, so i can modify the number of times to ask for
* a password, by editing only in one place (at the top). */
if (times < NTIMES) {
printf("login successful!\n");
return 0; /* successful exit code, see exit(3) for details */
} else {
printf("login failed.\n");
return 1; /* some error happened */
}
}