Script started on Wed Oct 21 17:34:39 2026
Restored session: Mon Oct 19 18:47:00 EDT 2026
macbook:logs> cat ~/Desktop/q15.txt 
    char *duplicate(const char *p) {
        char *q;
        strcpy(q,p);
        return q;
    }
Is the problem with the above code:
a). "const" is not a keyword in C
b). "strcpy" cannot take pointers as args
c). q does not point to allocated memory
d). You cannot return a pointer from a function
macbook:logs> echo s1 = computer
s1 = computer
macbook:logs> echo s1 = computerscience
s1 = computerscience
macbook:logs> echo "strlen(s1) = 15"
strlen(s1) = 15
macbook:logs> ech "15 - 6 = 9"
zsh: command not found: ech
macbook:logs> echo "15 - 6 = 9"
15 - 6 = 9
macbook:logs> echo "s1 = computers_ience (underscore is for null char)"
s1 = computers_ience (underscore is for null char)
macbook:logs> cd ../programs/C_ch13
macbook:C_ch13> cat what_will_be.c
#include <stdio.h>
#include <string.h>

int main() {

char s1[100];
char s2[100];

strcpy(s1,"computer");
strcpy(s2,"science");

printf("s1 is [%s]\n", s1);
printf("s2 is [%s]\n", s2);

if (strcmp(s1,s2) < 0)
strcat(s1,s2);
else
strcat(s2,s1);

printf("After strcat\n");
printf("s1 is [%s]\n", s1);
printf("s2 is [%s]\n", s2);


s1[strlen(s1) - 6]='\0';
printf("After inserting null char\n");
printf("s1 is [%s]\n", s1);
printf("s2 is [%s] (same as before) \n", s2);

return 0;}

macbook:C_ch13> gcc what_will_be.c
macbook:C_ch13> ./a.out
s1 is [computer]
s2 is [science]
After strcat
s1 is [computerscience]
s2 is [science]
After inserting null char
s1 is [computers]
s2 is [science] (same as before) 
macbook:C_ch13> cd ../C_ch2
macbook:C_ch2> cat typedef.c
/* 
  typedef allows for user-defined types
*/

#include <stdio.h>

typedef short int  Int16;

int main (void) {

   Int16 a = 4;

   printf("the number is %d\n", a); 

   return 0;
}


macbook:C_ch2> cd ../C_ch16
macbook:C_ch16> cat C_ch16_3b.c
#include <stdio.h>

typedef struct {
    int number;
    char name[NAME_LEN + 1];
    int on_hand;
} Part;

int main() { 
    Part part1, part2;

    part1.number = 3;
    part1.name = "wrench"; // Why does this not work?
    part1.on_hand = 1;
  

    printf("Part number %d with name \"%s\" has %d units here.\n",
      part1.number, part1.name, part1.on_hand);
    
    return 0;
}

macbook:C_ch16> gcc C_ch16_3b.c
C_ch16_3b.c:5:15: error: use of undeclared identifier 'NAME_LEN'
    5 |     char name[NAME_LEN + 1];
      |               ^
1 error generated.
macbook:C_ch16> cat C_ch16_3b.c
#include <stdio.h>

#define   NAME_LEN  100

typedef struct {
    int number;
    char name[NAME_LEN + 1];
    int on_hand;
} Part;

int main() { 
    Part part1, part2;

    part1.number = 3;
    part1.name = "wrench"; // Why does this not work?
    part1.on_hand = 1;
  

    printf("Part number %d with name \"%s\" has %d units here.\n",
      part1.number, part1.name, part1.on_hand);
    
    return 0;
}

macbook:C_ch16> gcc C_ch16_3b.c
C_ch16_3b.c:15:16: error: array type 'char[101]' is not assignable
   15 |     part1.name = "wrench"; // Why does this not work?
      |     ~~~~~~~~~~ ^
1 error generated.
macbook:C_ch16> cat C_ch16_3b.c
#include <stdio.h>

#define   NAME_LEN  100

typedef struct {
    int number;
    char name[NAME_LEN + 1];
    int on_hand;
} Part;

int main() { 
    Part part1, part2;

    part1.number = 3;
    strncpy(part1.name, "wrench", NAME_LEN); 
    part1.on_hand = 1;
  

    printf("Part number %d with name \"%s\" has %d units here.\n",
      part1.number, part1.name, part1.on_hand);
    
    return 0;
}

macbook:C_ch16> gcc C_ch16_3b.c
C_ch16_3b.c:15:5: error: call to undeclared library function 'strncpy' with type 'char *(char *, const char *, unsigned long)'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
   15 |     strncpy(part1.name, "wrench", NAME_LEN); 
      |     ^
C_ch16_3b.c:15:5: note: include the header <string.h> or explicitly provide a declaration for 'strncpy'
1 error generated.
macbook:C_ch16> gcc C_ch16_3b.c
macbook:C_ch16> cat C_ch16_3b.c
#include <stdio.h>
#include "strings.h"

#define   NAME_LEN  100

typedef struct {
    int number;
    char name[NAME_LEN + 1];
    int on_hand;
} Part;

int main() { 
    Part part1, part2;

    part1.number = 3;
    strncpy(part1.name, "wrench", NAME_LEN); 
    part1.on_hand = 1;
  

    printf("Part number %d with name \"%s\" has %d units here.\n",
      part1.number, part1.name, part1.on_hand);
    
    return 0;
}

macbook:C_ch16> gcc C_ch16_3b.c
macbook:C_ch16> ./a.out
Part number 3 with name "wrench" has 1 units here.
macbook:C_ch16> gcc C_ch16_3c.c
macbook:C_ch16> cat C_ch16_3c.c 
#include <stdio.h>
#include "strings.h"

#define   NAME_LEN  100

typedef struct {
    int number;
    char name[NAME_LEN + 1];
    int on_hand;
} Part;

int main() { 
    Part part1, part2;

    part1.number = 3;
    strncpy(part1.name, "wrench", NAME_LEN); 
    part1.on_hand = 1;
    part2.number = 4;
    strncpy(part2.name, "hammer", NAME_LEN); 
    part2.on_hand = 8;
  

    printf("Part number %d with name \"%s\" has %d units here.\n",
      part1.number, part1.name, part1.on_hand);
    printf("Part number %d with name \"%s\" has %d units here.\n",
      part2.number, part2.name, part2.on_hand);
    
    return 0;
}

macbook:C_ch16> ./a.out
Part number 3 with name "wrench" has 1 units here.
Part number 4 with name "hammer" has 8 units here.
macbook:C_ch16> cat struct_return.c
#include <stdio.h>
#include <string.h>
#define NAME_LEN  100

typedef struct {
  int number;
  char name[NAME_LEN + 1];
  int on_hand;
} Part;

Part part1, part2;

Part build_part(int number,
                const char * name, int on_hand)
{
    Part p;
    p.number = number;
    strcpy(p.name, name);
    p.on_hand = on_hand;
    return p;
}

int main() {

  part1 = build_part(3, "abc", 1);
  printf("  number %d\n", part1.number);
  printf("  name [%s]\n", part1.name);
  printf("  onhand %d\n", part1.on_hand);
  

  return 0;
}
macbook:C_ch16> gcc struct_return.c
macbook:C_ch16> ./a.out
  number 3
  name [abc]
  onhand 1
macbook:C_ch16> exit

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Script done on Wed Oct 21 18:42:01 2026