CODEWITHSUNDEEP
cstringstrcmp
Christian Halim
Christian Halim

Reputation: 117

Why can't i compare this two string ? The string input is the same, but it always return false

I got the random password generator program from here https://codereview.stackexchange.com/questions/138703/simple-random-password-generator And then I wanted to make a simple password program. Which generate 3 random char and uses sprint to combine "REG-" with the 3 random char. 

REG-xxx

but the program doesn't compare it the way I expect it to do so. Do I miss some unexpected elements in the array ? Because I have read that char arrays counts newline or space as its elements too, Thanks in advance. Here's my code

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

int main(){

    int i;
    srand((unsigned int)(time(NULL)));
    char pass[6];
    char codebook[10];
    char password[10];

    printf("Press enter to get a three-character password\n");
    getchar();

    for (i = 0; i < 1; i++) {
        pass[i] = rand() % 9;
        char capLetter = 'A' + (rand() % 26);
        pass[i + 2] = capLetter;
        char letter = 'a' + (rand() % 26);
        pass[i + 3] = letter;
        printf("%d%c%c\n", pass[i], pass[i + 2], pass[i + 3]);
        sprintf(codebook, "REG-%d%c%c\n", pass[i], pass[i+2], pass[i + 3]);
    }
    system("pause");
    printf("%s\n", codebook);
    fflush(stdin);
    printf("Enter the password: ");
    scanf("%s", password);
    printf("\n%s\n", password);
    printf("%s\n", codebook);
    system("pause");
    if(strcmp(codebook , password) == 0){
        printf("password is correct\n");
    } else{
        printf("password is false\n");
    }


    return 0;
}

Upvotes: 1

Views: 41

Answers (1)

Yunnosch
Yunnosch

Reputation: 26703

Here you print a newline into the password

sprintf(codebook, "REG-%d%c%c\n", pass[i], pass[i+2], pass[i + 3]);

You can later not enter that newline into the password and hence the comparision fails.

Changing to 

sprintf(codebook, "REG-%d%c%c", pass[i], pass[i+2], pass[i + 3]);

solves the problem.

To find this kind of problem with whitespace in strings, I recommend to debug by printing the strings framing them in "impossible" but printable characters. As I recomended in a comment, I found the problen by introducing some additional prints (or modifying existing ones):

In this case, the helpful one was directly after the problematic sprintf():

printf("#%s#\n", codebook);

Upvotes: 1

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