A null character is automatically appended to the end of the
    output string. Consider the following example of a conversion
    specification:

    #include <stdio.h>

    main()
    {
       int  temp = 4, temp2 = 17;
       char s[80];

       sprintf(s, "The answers are %d, and %d.", temp, temp2);
    }

    In this example, character string s has the following contents:

    The answers are 4, and 17.