Script started on Wed Oct 28 17:29:48 2026
Restored session: Mon Oct 26 18:45:10 EDT 2026
macbook:logs> cd ../programs/C_ch17
macbook:C_ch17> cat ~/Desktop/q17.txt 
A struct with four floats has a size of 16. Should a union of four floats also have a size of 16?

macbook:C_ch17> cat malloc_ex1.c 
#include <stdio.h>
#include <stdlib.h>

int main() {
  char *p;

  p = malloc(10000);
  if (p == NULL) {
    printf("Could not allocate memory\n");
    exit(0);
  }

  printf("Memory allocation worked\n");
  free(p);

  return 0;
}
macbook:C_ch17> gcc malloc_ex1.c 
macbook:C_ch17> ./a.out
Memory allocation worked
macbook:C_ch17> cat malloc_ex2.c 
#include <stdio.h>
#include <stdlib.h>

int main() {

  //char p[] = malloc(10000);
  char p[10000];

  p = malloc(10000);

  // this does not really work
  if (p[0] == NULL) {
    printf("Could not allocate memory\n");
    exit(0);
  }

  printf("Memory allocation worked\n");
  free(p);

  return 0;
}
macbook:C_ch17> cat C_ch17_10.c

#include <stdio.h>

int main() { 

  char *p = malloc(1024);
  if (p == NULL) {
     printf("Could not allocate memory\n");
     exit(2);
  }

  fp = fopen("test.txt", "r");
  // Always check to see if the command worked.
  if (fp == NULL) {
    // It did not work, so quit.
    printf("Error: fopen command failed\n");
    exit(1);
  }
  // .. do some file stuff

  // Close the stream
  fclose(fp);

  free(p);


  return 0;
}
macbook:C_ch17> gcc C_ch17_10.c
C_ch17_10.c:6:13: error: call to undeclared library function 'malloc' with type 'void *(unsigned long)'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
    6 |   char *p = malloc(1024);
      |             ^
C_ch17_10.c:6:13: note: include the header <stdlib.h> or explicitly provide a declaration for 'malloc'
C_ch17_10.c:9:6: error: call to undeclared library function 'exit' with type 'void (int) __attribute__((noreturn))'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
    9 |      exit(2);
      |      ^
C_ch17_10.c:9:6: note: include the header <stdlib.h> or explicitly provide a declaration for 'exit'
C_ch17_10.c:12:3: error: use of undeclared identifier 'fp'
   12 |   fp = fopen("test.txt", "r");
      |   ^
C_ch17_10.c:14:7: error: use of undeclared identifier 'fp'
   14 |   if (fp == NULL) {
      |       ^
C_ch17_10.c:22:10: error: use of undeclared identifier 'fp'
   22 |   fclose(fp);
      |          ^
C_ch17_10.c:24:3: error: call to undeclared library function 'free' with type 'void (void *)'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
   24 |   free(p);
      |   ^
C_ch17_10.c:24:3: note: include the header <stdlib.h> or explicitly provide a declaration for 'free'
6 errors generated.
macbook:C_ch17> vi C_ch17_10.c  
macbook:C_ch17> gcc C_ch17_10.c
C_ch17_10.c:13:3: error: use of undeclared identifier 'fp'
   13 |   fp = fopen("test.txt", "r");
      |   ^
C_ch17_10.c:15:7: error: use of undeclared identifier 'fp'
   15 |   if (fp == NULL) {
      |       ^
C_ch17_10.c:23:10: error: use of undeclared identifier 'fp'
   23 |   fclose(fp);
      |          ^
3 errors generated.
macbook:C_ch17> vi C_ch17_10.c 
macbook:C_ch17> gcc C_ch17_10.c
macbook:C_ch17> cat C_ch17_10.c

#include <stdio.h>
#include <stdlib.h>

int main() { 

  FILE *fp;

  char *p = malloc(1024);
  if (p == NULL) {
     printf("Could not allocate memory\n");
     exit(2);
  }

  fp = fopen("test.txt", "r");
  // Always check to see if the command worked.
  if (fp == NULL) {
    // It did not work, so quit.
    printf("Error: fopen command failed\n");
    exit(1);
  }
  // .. do some file stuff

  // Close the stream
  fclose(fp);

  free(p);


  return 0;
}
macbook:C_ch17> ./a.out
macbook:C_ch17> vi C_ch17_10.c 
macbook:C_ch17> gcc C_ch17_10.c
macbook:C_ch17> ./a.out        
The first up to 255 chars are: [This is a list of courses.
]
macbook:C_ch17> cat C_ch17_10.c 

#include <stdio.h>
#include <stdlib.h>

int main() { 

  FILE *fp;

  char *p = malloc(1024);
  if (p == NULL) {
     printf("Could not allocate memory\n");
     exit(2);
  }

  fp = fopen("test.txt", "r");
  // Always check to see if the command worked.
  if (fp == NULL) {
    // It did not work, so quit.
    printf("Error: fopen command failed\n");
    exit(1);
  }
  // .. do some file stuff
  char buff[255+1]; // n=255
  fgets(buff, 255, (FILE*)fp);

  printf("The first up to 255 chars are: [%s]\n", buff);
  

  // Close the stream
  fclose(fp);

  free(p);


  return 0;
}
macbook:C_ch17> vi C_ch17_10.c 
macbook:C_ch17> man fgets
macbook:C_ch17> gcc C_ch17_10.c
C_ch17_10.c:26:40: warning: comparison between pointer and integer ('char *' and 'int') [-Wpointer-integer-compare]
   26 |   while ((fgets(buff, 255, (FILE*)fp)) != EOF) {
      |          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^  ~~~
1 warning generated.
macbook:C_ch17> vi C_ch17_10.c 
macbook:C_ch17> gcc C_ch17_10.c
macbook:C_ch17> ./a.out
file: [This is a list of courses.
]
file: [CSC 1010 - COMPUTERS & APPLICATIONS
]
macbook:C_ch17> cat C_ch17_10.c

#include <stdio.h>
#include <stdlib.h>

int main() { 

  FILE *fp;

  char *p = malloc(1024);
  if (p == NULL) {
     printf("Could not allocate memory\n");
     exit(2);
  }

  fp = fopen("test.txt", "r");
  // Always check to see if the command worked.
  if (fp == NULL) {
    // It did not work, so quit.
    printf("Error: fopen command failed\n");
    exit(1);
  }

  // .. do some file stuff
  char buff[255+1]; // n=255

  while ((fgets(buff, 255, (FILE*)fp)) != NULL) {
    //fgets(buff, 255, (FILE*)fp);

    printf("file: [%s]\n", buff);
  } 

  // Close the stream
  fclose(fp);

  free(p);


  return 0;
}
macbook:C_ch17> cat ~/Desktop/q18.txt 

Suppose that we have the code:
    enum {ASH, MAPLE, OAK, HICKORY};

    int mytree = MAPLE;

What value does "mytree" have?

a. -1
b. 0
c. 1
d. undefined
e. this will cause a compiler error

macbook:C_ch17> exit

Saving session...
...saving history...truncating history files...
...completed.
Deleting expired sessions...       1 completed.

Script done on Wed Oct 28 18:47:00 2026