How do I remove overflow characters or append characters in a given string in C?

I basically want to have an arbitrary length string but a fixed size output string. So if I assign x a string of 10 characters, I want to end up with a string of 5 characters at the second printf. And if x is 3 characters, I wanna add on blanks to make the string 5 characters. Here is my code so far, but its not working because I can't even access an index, it segfaults;

int main()
{
    char x[] = "d dddddddd";
    printf(x);
    printf("");
    // separate
    printf(x[1]);
    return 0;
}

Thanks, I wonder whether this is possible in C, but you could also attempt it in C++

EDIT: My 2 codes are here, they both overflow;

char first[40];
char g[] = "     Level %d      %d Fruit    %d:%d      ";
char d[41] = {0};   
strncpy(d, g, 40);
if(strlen(d) < 40) {
    for(i = strlen(d); i < 40; i++) {
        d[i] = ' ';
    }
}
n = sprintf(first, d, gol, gift, minutes, secs );

2nd strategy;

char first[40];
char b[40];
strncpy(b, g, sizeof(b));
fgets(b, 40, stdin);                          
n = sprintf(first, b, gol, gift, minutes, secs );

Print my n onto the game's screen, I get my text and some unknown characters following. Sorry that I can't post the whole game code because its 4000 lines long split in 10 files. I wold appreciate a completely different way of getting a string of only 40 characters from a string of more characters.