COMP1721 - Higher Computing 1B

1. ---

   T_INT
   T_IDENTIFIER
   T_SEMICOLON
   T_IDENTIFIER
   T_ASSIGNMENT
   T_CONSTANT
   T_SEMICOLON
   T_PUTI
   T_LEFT_PARENTHESIS
   T_IDENTIFIER
   T_RIGHT_PARENTHESIS
   T_SEMICOLON
   

   ---

   For the T_IDENTIFIER tokens the text() will be "answer".

   For the T_CONSTANT token the int_value will be 42.

2. ---

   #include <stdio.h>
   #include <stdlib.h>
   #include "cavy_syntax.h"
   
   char *source_filename;
   
   void usage(char *myname);
   void count_semicolons(void);
   
   void
   usage(char *myname) {
       fprintf(stderr, "Usage: %s [simple-C-file]\n", myname);
       exit(1); 
   }
   
   
   int
   main(int argc, char *argv[]) {
       if (argc == 1) {
           source_filename = "";
           open_lexical_analysis(stdin);
       } else if (argc == 2) {
           FILE *f;
           source_filename = argv[1];
           if ((f = fopen(argv[1], "r")) == NULL) {
               fprintf(stderr, "%s: cannot open file: %s\n", argv[0], source_filename);
               exit(1);
           }
           open_lexical_analysis(f);
       } else {
           usage(argv[0]);
       }
       
       /*
        * code above here is distributed with assignment 2
        */
       count_semicolons();
       return 0;
   }
   void
   count_semicolons(void) {
       int semicolon_count = 0;
   
       for (;;) {
           token *t = get_token();
           if (t->type == T_EOF)
               break;
           if (t->type == T_SEMICOLON)
               semicolon_count++;
       }
       
       printf("%d\n", semicolon_count);
   }
   

   ---

3. typedef struct variable variable;
   
   struct variable {
       char        *name;
       variable    *next;
       int         value;
   };
   /*
    * Find the int variable associated with a name.
    *
    * A pointer to the int variable is returned.
    *
    * If the name has not been previously associated
    * with an int variable, a variable is created
    * and initialized to zero.
    */
   
   int *
   lookup_variable(char *name) {
       static variable *list;
       variable *v;
       
       for (v = list; v != NULL; v = v->next)
           if (strcmp(name, v->name) == 0)
               return &(v->value);
       
       if ((v = malloc(sizeof *v)) == NULL) {
           fprintf(stderr, "Out of memory\n");
           exit(1);
       }
       v->name = name;
       v->next = list;
       v->value = 0;
       list = v;
       return &(v->value);
   }