Unexpected Output plus segmentation error with my C program

Question

I am trying to learn programming and was trying the following code in C. However, As you can see below I am not getting the expected output and I am getting a segmentation error while trying out solutions :

I feel I am doing something wrong with the declaration of First name or something. But not able to figure it out.

My Code:

#include <stdio.h>

int main(void){
    char first_name;
    printf("Enter your name: \n");
    scanf("%c", &first_name);
    printf("Hello, %c", first_name);
}

Actual Output

This is the output I am currently getting:

Enter your name: 
asdasfasf
Hello, a

Expected Output

Enter your name: 
asdasfasf
Hello, asdasfasf

Answer 1

Here is my answer

#include <stdio.h>

int main(void){    
        char first_name[100] = {0}; 
        printf("Enter your name:(Max length is 99)\n"); 
        scanf("%99s", first_name); 
        printf("Hello, %s\n", first_name); 
}

Run it will output

Enter your name:(Max length is 99)
asdasfasf
Hello, asdasfasf

Here is my other solution that can handle @Andreas Wenzel point out that "it is possible for a first name to consist of several words":

#include <stdio.h>

int main()
{
    char first_name[100] = {0};
    char c = 0;
    printf("Enter your name:(Max length is 99)\n");

    // read 99 times, once a character, it suspend when read '\n', 
    // otherwise save to first_name array  when read character.
    for(int m = 0; m < 99; m++){
        if((c = getchar()) != '\n'){
            first_name[m] = c;
        }else{
            break;
        }
    }

    printf("Hello, %s\n", first_name);
}

Run it will output

Enter your name:(Max length is 99)
asdsfd  
Hello, asdsfd

or like this:

Enter your name:(Max length is 99)
dsds dggffgg
Hello, dsds dggffgg

or also like this:

Enter your name:(Max length is 99)
ssd dsdfds dsfdfgfdg ddfdsfdf sfsdfsdf
Hello, ssd dsdfds dsfdfgfdg ddfdsfdf sfsdfsdf

Answer 2

Using scanf with the %c conversion format specifier will only read a single character.

In order to read a whole word, you can use the %s specifier instead. However, in the English langauge, it is possible for a first name to consist of several words, such as John Paul. In that case, "Paul" is not a middle name, but part of the first name. With the input "John Paul", scanf would only read "John" from the input stream and leave " Paul" on the input stream. This would probably be undesirable.

For this reason, it would probably be better to read and store a whole line of input, instead of only a single word. Although this is also possible with scanf, I recommend to use the function fgets instead.

When reading in a string consisting of several characters, you must provide a pointer to a memory location that has sufficient allocated space for storing the string. Providing a pointer to a single char is not sufficient, as such a memory location is only able to store a single character. This means that the memory location is only able to store an empty string consisting only of a null terminating character.

One simple way of allocating sufficient space for storing a string is to declare a char array. When passing such an array to a function, the array will automatically decay to a pointer to the first element of the array.

Here is an example:

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

int main( void )
{
    char first_name[200];

    //prompt user for input
    printf( "Enter your name: " );

    //read one line of input
    if ( fgets( first_name, sizeof first_name, stdin ) == NULL )
    {
        fprintf( stderr, "Input error!\n" );
        exit( EXIT_FAILURE );
    }

    //remove newline character from the input, if it exists,
    //by overwriting it with a null terminating character
    first_name[strcspn(first_name,"\n")] = '\0';

    //print back input to user
    printf( "Hello, %s.\n", first_name );
}

This program has the following behavior:

Enter your name: John Paul
Hello, John Paul.