Class 17: Structures

Question 1

struct book {
char title[MAXTITL];
char author[MAXAUTL];
float value;
};
What is the TAG for this structure declaration?

Answer 1

Book

Question 2

struct book {
char title[MAXTITL];
char author[MAXAUTL];
float value;
};
How would you declare structure of this data type?

Answer 2

struct book library;

Question 3

Declaring multiple structures of same type

Answer 3

struct book doyle, panshin, *ptbook

Question 4

How to declare structure variable after the structure bracket

Answer 4

struct book {
char title[MAXTITL];
char author[AXAUTL];
float value;
} library; /* follow declaration with variable name */

Question 5

How to intialize a structure variable given the follwing structure

struct book {
char title[MAXTITL];
char author[AXAUTL];
float value;
} ;

Answer 5

struct book library = {
“The Pious Pirate and the Devious Damsel”,
“Renee Vivotte”,
1.95
};
MUST BE SEPARATED BY COMMA

Question 6

struct book {
char title[MAXTITL];
char author[AXAUTL];
float value;
} ;
How to access structure members

Answer 6

struct book library;
library.value

Question 7

Which is correct
scanf(“%f”,&library.value) or
scanf(“%f”,&(librarby.value))

Answer 7

Second option because & has higher precedence than dot operator

Question 8

Is this valid way to initialize a structures variable?

struct book gift = { .value = 25.99,
.author = “James Broadfool”,
.title = “Rue for the Toad”};

Answer 8

Yes

Question 9

How to declare an array of structures

Answer 9

struct book library[MAXBKS]
library[0].value;

Question 10

struct guy { // second structure
struct names handle; // nested structure
char favfood[LEN];
char job[LEN];
float income;
};

Answer 10

This structure contains a nested structure called handle. The name structure should be declared above the structure guy

Question 11

struct guy *him

Answer 11

Pointer to structure guy

Question 12

Suppose you have struct guy *him

Answer 12

him = &fellow[0]
him–>income = (*him).income

Question 13

o_data = n_data; // assigning one structure to another

Answer 13

This causes each member of n_data to be assigned the value of the corresponding member of 0_data This works even if a member happens to be an array. They must be structures of the SAME TYPE

Question 14

Strict{
Int a;
Float b;
}x;

Strict{
Int a;
Float b;
}y[10], *z;

Z = &x;
Y[2] = x;
Are these valid statements?

Answer 14

No because even though we can tell these two structures are the same, the compiler has not way of recognizing that these structures are identical, so they are treated as different. And you cannot have two different data types equal to each other!!!

Question 15

Typedef long long lol;
Typedef unsigned Int unit;

Ll long_var;
Unint count;

Answer 15

1. ll var1 declares var1 as long long
2. Unint count declares count as unsigned int

Question 16

Typedef strict{
Int a;
Int b;
}Simple;

Or
Typedef struct Simple{

Question 17

Typedef strict{
Int a;
Int b;
}Simple;

Or
Typedef struct Simple{
Int a;
Float;
}

How would you declare variables of this structure?

Answer 17

Simple x, y[10], *z;

Question 18

What should you do if you want to use particular structure type throughout a source file?

Answer 18

You should use Typedef or struct declaration WITH a tag BEFORE MAIN. (Lab4) This is necessary to give file scope to the type created with Typedef or struct tag.

Question 19

What is you want to use a particular structure in more than once source file?

Answer 19

You should put the tag declaration in a header file. Then you can use the #include the header file with the declaration whenever it is needed.

Question 20

Can structure members have identical names to members of a structure of different type?

Answer 20

Yes
Struct S_2{
Int memebr1;
Int member2
Struct *S_2 member3;
Int member4[45]
};

Question 22

How to directly access members of a structure??

Answer 22

THe dot operator

Question 23

If we have a pointer to a structure, how can we access the members?

Answer 23

-> : ptr->first_name
Or (*ptr).first_name

1st method is more common

Question 24

Op1->op2->op3 is equivalent to?

Answer 24

(((op1).op2).op3)

Question 25

Can you have a strucutre member of same type in a strucutre?

Answer 25

Not because the problem is infinite recursion. The compiler would have to allocate infinite amount of storage. Instead we can declare a member pointer (ex: struct *S_2 member). The compiler can allocate space for pointer to structure which requires finite amount of space

Question 26

Initialize the following structure as an array

Struct Init_example{
Int a;
Short b[10];
Simple c;
} y = {
10,
{1,2,3,4,5},
{25,1.9}
};

• Intial values for the members MUST IN THE ORDER GIVEN BY MEMBER LIST

Answer 26

Or we can have

Struct y = {
10,
{1,2,3,4,5},
{25,1.9}
}

Question 27

If we have two structures of x and y that are the same structure, can set x = y

Answer 27

Yes, since x and y have been declared of the same type, we can assign y to x by saying x = y. This assigns each member of y to the corresponding member of x!!

Question 28

How shoudlsturcutres be passed into functions

Answer 28

In C, parameters are passed by value so if the strucutre is large of of the values of all the members in the structure will have to be COPIED and pushed onto the stack when the function is called. WE SHOULD PASS a pointer instead because only the values of the pointer is passed rather than copies of all the values in the structure

Question 29

Const keyword

Int func1(int const *ptr){}

Function1 will not be able to change the values in the array or structure

Answer 29

Unless the functions needs to change values using the pointer, we should declare the parameter with const to indicate the the value(s) pointer to by the parameter WILL NOT CHANGE.

Question 30

Int const *ptr

Const means that the value the pointer is pointing to CANNOT CHANGE. You can READ the value of the integer but you cannot modify it

Answer 30

So int const *ptr is a pointer to constant integer