Scanf doesnt take more than 4 characters in a const char array - C

Question

I have a really weird bug. If I write a name which contains more than 4 characters, the printf will only output the first 4 characters.

Important note: I am not allowed to use any other library than stdio.h and I am not allowed to use anything else than scanf for input and printf for output. Moreover I am not allowed to modify the paramater list of the functions and I have to use const char. The code runs on putty via ssh on a unix system.

My code and the input/output are below. In addition, the while loop has a bug too ._.

#include <stdio.h>

int searchCharacters(const char*, char);
int getLength(const char*);

int main() {

    char yesNo;
    int end = 0;
    const char name[] = {""};

    printf("please enter a name: ");
    scanf("%s", name);
    int length = getLength(name);
    printf("\n%s has a length of %i", name, length);
    fflush(stdin);

    while(end != 1) {
        printf("\n\nWould you like to search a character in %s (y / n)?", name);
        scanf(" %c", &yesNo);

        switch(yesNo) {
            case 'y':
                printf("\nPlease enter a character: ");
                char searchingCharacter;
                scanf("%c", &searchingCharacter);
                int numberOfCharacters = searchCharacter(name, searchingCharacter);
                printf("\nThe letter %c is %i-times", searchingCharacter, numberOfCharacters);
                break;
            case 'n':
                printf("\nGood bye!");
                end++;
                break;
        }
    }
    return 0;
}

int searchCharacter(const char s[], char c) {
    int numberOfIterations = getLength(s);
    int numberOfCharacters = 0;
    int i;

    for (int i = 0; i < numberOfIterations; i++) {
        if (s[i] == c) {
            numberOfCharacters++;
        }
    }
    return numberOfCharacters;
}

int getLength(const char s[]) {
    int i = 0;
    while(s[i++]);

    return (i - 1);
}

Input/Output:
    please enter a name: abcdefg

    abcd has a length of 7 characters.

    Would you like to search a character in abcd (y / n)? y

<-------------- AUTOMATIC/BUG WHILE LOOP --------------------------->

    Please enter a character:
    The letter
      is 0-times.

</--------------AUTOMATIC/BUG WHILE LOOP---------------------------->

    Would you like to search a character in abcd (y / n)? n

    Good bye!

Still the same result. What do you mean with "that too it is const"? — Andrew
You would have a buffer overflow in these lines const char name[] = {""}; printf("please enter a name: "); scanf("%s", name); were it not for the fact that name is const and hence should not be modified at all. I would start with fixing these bugs first and then worry about the program not working as expected. — Tanveer Badar
Yeah, I am trying but I have absolutely no clue how.. Im new to c and my prof says we have to use const char (or did I listened wrong?). At least he says the parameter list has to have const char — Andrew
Further to what @TanveerBadar wrote, your compiler should have warned you about that first line of code. Don't ignore the compiler warnings but instead fix them all up. If your compiler did not warn you then you need to turn up the warning level. — kaylum

Andrew Andrew · Accepted Answer · 2019-11-24T11:50:36

So, here is a possible answer:

"Change const char name[] to char name[100]" (from @kaylum)

"Change scanf("%c", &searchingCharacter) --> scanf(" %c", %searchingCharacters) to consume new line in input stream" (from @user3121023)

Here is the full code:

#include <stdio.h>

int searchCharacters(const char*, char);
int getLength(const char*);

int main() {

    char yesNo;
    int end = 0;
    char name[100]; <-- Changed -->

    printf("please enter a name: ");
    scanf("%99s", name);
    fflush(stdin);
    int length = getLength(name);
    printf("\n%s has a length of %i", name, length);

    while(end != 1) {
        printf("\n\nWould you like to search a character in %s (y / n)?", name);
        scanf("%c", &yesNo); <-- Changed -->

        switch(yesNo) {
            case 'y':
                printf("\nPlease enter a character: ");
                char searchingCharacter;
                scanf(" %c", &searchingCharacter); <-- Changed -->
                int numberOfCharacters = searchCharacter(name, searchingCharacter);
                printf("\nThe letter %c is %i-times", searchingCharacter, 
                numberOfCharacters);
                break;
            case 'n':
                printf("\nGood bye!");
                end++;
                break;
        }
    }
    return 0;
}

int searchCharacter(const char s[], char c) {
    int numberOfIterations = getLength(s);
    int numberOfCharacters = 0;
    int i;

    for (int i = 0; i < numberOfIterations; i++) {
        if (s[i] == c) {
            numberOfCharacters++;
        }
    }
    return numberOfCharacters;
}

int getLength(const char s[]) {
    int i = 0;
    while(s[i++]);

    return (i - 1);
}

Input/Output:
    please enter a name: abcdefg

    abcdefg has a length of 7 characters. <-- Working/Changed -->

    Would you like to search a character in abcd (y / n)? y

    Please enter a character: a <-- Working/Changed -->

    The letter a is 1-times. <-- Working/Changed -->

    Would you like to search a character in abcdefg (y / n)? n

    Good bye!

Scanf doesnt take more than 4 characters in a const char array - C

1 Answers