Add two strings in C

Question

How would I add a string to a string that I get from scanf?

Do this:

char animal[size];
scanf("%s", animal);

Then add "Is it a animal?" to whatever is input, then return the whole thing as animal again.

For example if I input 'duck' for animal, it will make animal return "Is it a duck?"

Also, should I add the ? to animal first then add "Is it a "?

Answer 1

Here is a quick and dirty working example of how this could be done.

However, it is not very safe/foolproof. E.g., you can easily overrun the animal buffer with scanf(). Also, if you change the format of the string in sprintf(), you'll need to make sure str has enough room.

#include <stdio.h>

int main()
{
    char animal[20];
    char str[29];
    animal[19] = 0; /* make sure animal is 0-terminated. Well, scanf() will 0-term it in this case anyway, but this technique is useful in many other cases.  */
    printf("Name the beast (up to 19 characters): ");
    scanf("%s", animal);
    sprintf( str, "Is it a %s?", animal );
    puts(str);
    return 0;
}

And here is a somewhat improved version. We make sure that we don't read more characters than the animal buffer can hold, define a pre-processor macro for the maximum animal name length for easier maintenance, trap the case when the user entered more characters than asked, get rid of the newline that terminates user input.

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

#define MAX_ANIMAL_NAME_LEN 9

int main()
{
    /* 1 char for 0-terminator + 1 to catch when a user enters too
       many characters. */
    char animal[MAX_ANIMAL_NAME_LEN + 2];
    char str[MAX_ANIMAL_NAME_LEN + 11];
    printf("Name the beast (up to %d characters): ", MAX_ANIMAL_NAME_LEN);
    fgets( animal, MAX_ANIMAL_NAME_LEN + 2, stdin );
    {
       /* fgets() may include a newline char, so we get rid of it. */
       char * nl_ptr = strchr( animal, '\n' );
       if (nl_ptr) *nl_ptr = 0;
    }
    if (strlen(animal) > MAX_ANIMAL_NAME_LEN)
    {
       fprintf( stderr, "The name you entered is too long, "
                        "chopping to %d characters.\n", MAX_ANIMAL_NAME_LEN );
       animal[MAX_ANIMAL_NAME_LEN] = 0;
    }
    sprintf( str, "Is it a %s?", animal );
    puts(str);

    return 0;
}

As other users have pointed out, strings in C, as the C language itself, can get fairly tricky pretty fast. Further improvements will be your homework. Search engines are your friends. Happy learning!

One treacherous pitfall you may want to beware is that there is still input to be read from STDIN if the user has typed more than fgets() wanted to accept. If you call fgets() or some other input function later on, you will read those extra characters, which is probably not what you wanted! Please see the following posts:

How to clear input buffer in C?

C: Clearing STDIN

Thanks to chux for pointing this out.

Answer 2

If you just want to display the message of "Is it a ___?" you can just output it like

char animal[size];
scanf("%s", animal);
printf("Is it a %s?", animal);

Answer 3

How would I add a string to a string that I get from a scanf?

Adding two different strings,.

#include <stdio.h>
#include <string.h>
int main(void)    
{
    char animal[20], text1[20] = "Is it a ";
    scanf("%11s", animal);
    strcat(text1, animal);
    printf("%s\n", text1);
    return 0;
}