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### Chapter 16

2. [was #2; modified]

(a)

```struct {
double real, imaginary;
} c1, c2, c3;
```

(b)

```struct {
double real, imaginary;
} c1 = {0.0, 1.0}, c2 = {1.0, 0.0}, c3;
```

(c) Only one statement is necessary:

```c1 = c2;
```

(d)

```c3.real = c1.real + c2.real;
c3.imaginary = c1.imaginary + c2.imaginary;
```

4. [was #4; modified]

(a)

```typedef struct {
double real, imaginary;
} Complex;
```

(b) `Complex c1, c2, c3;`

(c)

```Complex make_complex(double real, double imaginary)
{
Complex c;

c.real = real;
c.imaginary = imaginary;
return c;
}
```

(d)

```Complex add_complex(Complex c1, Complex c2)
{
Complex c3;

c3.real = c1.real + c2.real;
c3.imaginary = c1.imaginary + c2.imaginary;
return c3;
}
```

11. [was #10; modified] The `a` member will occupy 8 bytes, the union `e` will take 8 bytes (the largest member, `c`, is 8 bytes long), and the array `f` will require 4 bytes, so the total space allocated for `s` will be 20 bytes.

14. [was #12; modified]

(a)

```double area(struct shape s)
{
if (s.shape_kind == RECTANGLE)
return s.u.rectangle.height * s.u.rectangle.width;
else
}
```

(b)

```struct shape move(struct shape s, int x, int y)
{
struct shape new_shape = s;

new_shape.center.x += x;
new_shape.center.y += y;
return new_shape;
}
```

(c)

```struct shape scale(struct shape s, double c)
{
struct shape new_shape = s;

if (new_shape.shape_kind == RECTANGLE) {
new_shape.u.rectangle.height *= c;
new_shape.u.rectangle.width *= c;
} else

return new_shape;
}
```

15. [was #14]

(a) `enum week_days {MON, TUE, WED, THU, FRI, SAT, SUN};`
(b) `typedef enum {MON, TUE, WED, THU, FRI, SAT, SUN} Week_days;`

17. [was #16] All the statements are legal, since C allows integers and enumeration values to be mixed without restriction. Only (a), (d), and (e) are safe. (b) is not meaningful if `i` has a value other than 0 or 1. (c) will not yield a meaningful result if `b` has the value 1.

#### Answers to Selected Programming Projects

1. [was #6; modified]

```#include <stdio.h>

#define COUNTRY_COUNT \
((int) (sizeof(country_codes) / sizeof(country_codes[0])))

struct dialing_code {
char *country;
int code;
};

const struct dialing_code country_codes[] =
{"Brazil",               55}, {"Burma (Myanmar)",  95},
{"China",                86}, {"Colombia",         57},
{"Congo, Dem. Rep. of", 243}, {"Egypt",            20},
{"Ethiopia",            251}, {"France",           33},
{"Germany",              49}, {"India",            91},
{"Indonesia",            62}, {"Iran",             98},
{"Italy",                39}, {"Japan",            81},
{"Mexico",               52}, {"Nigeria",         234},
{"Pakistan",             92}, {"Philippines",      63},
{"Poland",               48}, {"Russia",            7},
{"South Africa",         27}, {"South Korea",      82},
{"Spain",                34}, {"Sudan",           249},
{"Thailand",             66}, {"Turkey",           90},
{"Ukraine",             380}, {"United Kingdom",   44},
{"United States",         1}, {"Vietnam",          84}};

int main(void)
{
int code, i;

printf("Enter dialing code: ");
scanf("%d", &code);

for (i = 0; i < COUNTRY_COUNT; i++)
if (code == country_codes[i].code) {
printf("The country with dialing code %d is %s\n",
code, country_codes[i].country);
return 0;
}

printf("No corresponding country found\n");
return 0;
}
```

3. [was #8]

```#include <stdio.h>

#define NAME_LEN 25
#define MAX_PARTS 100

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

int find_part(int number, const struct part inv[], int np);
void insert(struct part inv[], int *np);
void search(const struct part inv[], int np);
void update(struct part inv[], int np);
void print(const struct part inv[], int np);

/**********************************************************
* main: Prompts the user to enter an operation code,     *
*       then calls a function to perform the requested   *
*       action. Repeats until the user enters the        *
*       command 'q'. Prints an error message if the user *
*       enters an illegal code.                          *
**********************************************************/
int main(void)
{
char code;
struct part inventory[MAX_PARTS];
int num_parts = 0;

for (;;) {
printf("Enter operation code: ");
scanf(" %c", &code);
while (getchar() != '\n')   /* skips to end of line */
;
switch (code) {
case 'i': insert(inventory, &num_parts);
break;
case 's': search(inventory, num_parts);
break;
case 'u': update(inventory, num_parts);
break;
case 'p': print(inventory, num_parts);
break;
case 'q': return 0;
default:  printf("Illegal code\n");
}
printf("\n");
}
}

/**********************************************************
* find_part: Looks up a part number in the inv array.    *
*            Returns the array index if the part number  *
*            is found; otherwise, returns -1.            *
**********************************************************/
int find_part(int number, const struct part inv[], int np)
{
int i;

for (i = 0; i < np; i++)
if (inv[i].number == number)
return i;
return -1;
}

/**********************************************************
* insert: Prompts the user for information about a new   *
*         part and then inserts the part into the inv    *
*         array. Prints an error message and returns     *
*         prematurely if the part already exists or the  *
*         array is full.                                 *
**********************************************************/
void insert(struct part inv[], int *np)
{
int part_number;

if (*np == MAX_PARTS) {
printf("Database is full; can't add more parts.\n");
return;
}

printf("Enter part number: ");
scanf("%d", &part_number);
if (find_part(part_number, inv, *np) >= 0) {
return;
}

inv[*np].number = part_number;
printf("Enter part name: ");
printf("Enter quantity on hand: ");
scanf("%d", &inv[*np].on_hand);
(*np)++;
}

/**********************************************************
* search: Prompts the user to enter a part number, then  *
*         looks up the part in the inv array. If the     *
*         part exists, prints the name and quantity on   *
*         hand; if not, prints an error message.         *
**********************************************************/
void search(const struct part inv[], int np)
{
int i, number;

printf("Enter part number: ");
scanf("%d", &number);
i = find_part(number, inv, np);
if (i >= 0) {
printf("Part name: %s\n", inv[i].name);
printf("Quantity on hand: %d\n", inv[i].on_hand);
} else
}

/**********************************************************
* update: Prompts the user to enter a part number.       *
*         Prints an error message if the part can't be   *
*         found in the inv array; otherwise, prompts the *
*         user to enter change in quantity on hand and   *
**********************************************************/
void update(struct part inv[], int np)
{
int i, number, change;

printf("Enter part number: ");
scanf("%d", &number);
i = find_part(number, inv, np);
if (i >= 0) {
printf("Enter change in quantity on hand: ");
scanf("%d", &change);
inv[i].on_hand += change;
} else
}

/**********************************************************
* print: Prints a listing of all parts in the inv array, *
*        showing the part number, part name, and         *
*        quantity on hand. Parts are printed in the      *
*        order in which they were entered into the       *
*        array.                                          *
**********************************************************/
void print(const struct part inv[], int np)
{
int i;

printf("Part Number   Part Name                  "
"Quantity on Hand\n");
for (i = 0; i < np; i++)
printf("%7d       %-25s%11d\n", inv[i].number,
inv[i].name, inv[i].on_hand);
}
```