COMP1721 - Higher Computing 1B

1. #include <stdio.h>
   #include <stdlib.h>
   
   int
   main(int argc, char *argv[]) {
       int n, i;
       int *numbers;
   
       printf("How many numbers? ");
       scanf("%d", &n);
       numbers = malloc(n*sizeof (int));    
       if (numbers == NULL) {
           fprintf(stderr, "out of memory\n");
           exit(1);
       }
       for (i = 0; i < n; i++)
           scanf("%d", &numbers[i]);
       printf("In reverse order:\n");
       for (i = n - 1; i >= 0; i--)
           printf("%d\n", numbers[i]);
       return 0;
   }
   

2. #include <stdio.h>
   #include <stdlib.h>
   
   int
   main(int argc, char *argv[]) {
       int i;
       int *buffer;
       int buffer_length = 1024;
   
       /*
        * allocate initial buffer
        */
       buffer = malloc(buffer_length*sizeof (int));    
       if (buffer == NULL) {
           fprintf(stderr, "out of memory\n");
           exit(1);
       }
       for (i = 0; ; i++) {
           if (i >= buffer_length) {
               /*
                * buffer full - increase its size
                */
               buffer_length += 1024;
               buffer = realloc(buffer, buffer_length*sizeof (int));    
               if (buffer == NULL) {
                   fprintf(stderr, "out of memory\n");
                   exit(1);
               }
           }
           scanf("%d", &buffer[i]);
           if (buffer[i] < 0)
               break;
       }
           
       printf("In reverse order:\n");
       for (i--; i >= 0; i--)
           printf("%d\n", buffer[i]);
       return 0;
   }
   

3. #include <stdio.h>
   #include <string.h>
   #include <stdlib.h>
   
   /*
    * split a comma-separated string into sub-strings
    * return substrings in malloc'ed NULL terminated array
    */
   char **
   split(char *s) {
       char **substrings;
       char *p, *q;
       int n_substrings, i;
       
       /*
        * count how many substrings
        */
       n_substrings = 1;
       for (p = s; *p != '\0'; p++)
           if (*p == ',')
               n_substrings++;
       
       substrings = malloc((n_substrings + 1)*sizeof (char *));    
       if (substrings == NULL) {
           fprintf(stderr, "out of memory\n");
           exit(1);
       }
       
       p = s;
       for (i = 0; i < n_substrings; i++) {
            /*
             * calculate length of this substring
             */
           int substring_length = 0;
           for (q = p; *q != ',' && *q != '\0'; q++)
               substring_length++;
            /*
             * malloc space for this substring
             */
          substrings[i] = malloc((substring_length + 1)*sizeof (char));
           if (substrings[i] == NULL) {
               fprintf(stderr, "out of memory\n");
               exit(1);
           }
            /*
             * copy substring to malloc'ed space
             */
           strncpy(substrings[i], p, substring_length);
           substrings[i][substring_length] = '\0';
            /*
             * move p to start of next substring
             */
           p += substring_length + 1;
       }
       substrings[n_substrings] = NULL;
       return substrings;
   }
   
   enum {
       MAX_LINE = 1024
   };
   
   int
   main(int argc, char *argv[]) {
       int i;
       char line[MAX_LINE];
       char **substrings;
   
       printf("Enter a comma separated string: ");
       fgets(line, MAX_LINE, stdin);
       for (i = 0; i < MAX_LINE; i++)
           if (line[i] == '\n') {
               line[i] = '\0';
               break;
           }
       substrings = split(line);
       for (i = 0;; i++) {
           if (substrings[i] == NULL)
               break;
           printf("substring %d = '%s'\n", i, substrings[i]);
       }
        return 0;
   }