Class 7+: Catch Up Homework

1. The following picture shows a chunk of memory along with five char* variables, which point to various locations in that memory.

   

   a. What would printf("%s",p) print?
   
   b. What would printf("%s",q) print?
   
   c. What would printf("%s",r) print?
   
   d. What would printf("%s",s) print?
   
   e. What would printf("%s",t) print?
   
   	

2. The following code replaces any non-printable characters in a file with a "." character. The program is supposed to function such that with no command-line arguments it reads from stdin, while with a command-line argument it takes that argument as the name of a file from whence it takes its input. Add one line (where indicated) to make the code so that it actually works this way.

        FILE *fin;
        if (argc > 1)
        {
          fin = fopen(argv[1],"r");
        }
        else
        {
   
   Add here →
   
        }
        char c;
        while(fscanf(fin,"%c",&c) == 1)
        {
          if (isprint(c))
            printf("%c",c);
          else
            printf("%c",'.');
        }
   	

3. Let str be a string. Write a chunk of code that replaces all space characters in str with $ characters.

4. Write a function multiply with the following prototype

   char* multiply(char *s, int n);
   	

   that returns a string that is n copies of s back-to-back. The multiply function will have to allocate the array as well as populate it with chars.

5. Use man to lookup fgetc and ungetc. Now, explain what the following program does, and why it needs fgetc and ungetc.

   #include <stdio.h>
   #include <ctype.h>
   
   int main()
   {
     char c;
     int t = 0, n;
     while((c = fgetc(stdin)) && c != EOF)
     {
       if (isdigit(c))
       {
         ungetc(c,stdin);
         fscanf(stdin,"%i",&n);
         t += n;
       }
     }
     fprintf(stdout,"%i\n",t);
     return 0;
   }
   

   In case it helps, I'll give you an example of this program in action:

   bash$ echo "abc123efg456hij" | ./hw2
   579