In an Array worksheet we had four game score from four different players, which we read and printed in reverse order. Instead of defining Score1,Score2, Score3 and Score4, we defined one array that held all four scores, that is Score[4]. We grouped them in an array because all items were of the same data type and had a similar meaning, they were all game scores.

However what about the group of data items that are related but have different data types? For example, suppose that along with the game scores, we want to store the name of each player, the country from which they come and their ages. Here, the score is a float, the player and the country are character strings and the age is an integer. We would like to store these four items together as one unit and to handle and process them together as a group. In order to do this we can usestructure data type. The keyword use to define this data type is struct. For our needs, we can define the structure as shown below.

struct Participant

{

     char Name[20];

     char Country[25];

     float Score;

     int Age;

};

struct is a keyword and the Participant is a name or tag that we provided. All that we are doing is defining a structure calledstruct Participant. We are not creating a variable instead we are creating a new data type that includes or aggregate other C and C++ data types. You can think of this as a structure template from which structure variables may be defined. Any variable declared as being of this type will have these four parts that are called members of the structure.

Later in the C++ worksheet of this series we will add more features to structure templates and call them classes. Variables defined as classes will be called objects. Just as variables are created from data types or structure variables are created from structure definitions, objects are created from classes.

With arrays, we need to specify the subscript or the index to access one item inside the array. To access one item in a structure, we need to specify the name of the member. The order in which the structure members are defined is not important. The following code shows how structure variables are defined and initialized.

struct Participant Player1, Player2 = {"Korea","Kenya", 4.6, 19};

The following Figures try to show the defining two structure variables.

#include<stdio.h>

#include<string.h>

// Global definition

struct Mobile

{

     char Make[20];

     int Year;

};

// function prototype with structure return type

struct Mobile FindYear(char Name[ ]);

// function prototype with structures arguments passed

void PrintOldest(struct Mobile Auto1, struct Mobile Auto2);

void main(void)

{

     struct Mobile Car1, Car2;

      Car1 = FindYear("Toyota");

      Car2 = FindYear("Mustang");

      PrintOldest(Car1, Car2);

}

// this function receives one string that is the make of a car,

// reads in its year and returns them both as "struct Mobile"

struct Mobile FindYear(char Name[ ])

{

     struct Mobile Car;

      printf("What year is the %s? ", Name);

     // scanf("%d", &Car.Year);

      scanf_s("%d", &Car.Year, 1);

      printf("Car.Year = %d\n", Car.Year);

     // strcpy(Car.Make, Name);

      strcpy_s(Car.Make, sizeof(Car.Make), Name);

     return Car;

}

// this function receives two structures of type "struct Mobile"

// and prints the year of the oldest car. It returns nothing.

void PrintOldest(struct Mobile Auto1, struct Mobile Auto2)

{

     if(Auto1.Year < Auto2.Year)

            printf("The oldest car is the %s\n", Auto1.Make);

     elseif(Auto1.Year > Auto2.Year)

            printf("The oldest car is the %s\n", Auto2.Make);

     else

            printf("They are both the same age!\n");

}

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struct Data Type Practices

1. Let us introduce two new functions intended for strings. You may enter “You’re making me blue” and then enter “All my loving”. Show the output and answer the questions.

#include<stdio.h>

void main()

{

  char a[25], b[25];

   puts("Name your favorite song title: ");

  // gets(a);

   gets_s(a, 25);

   puts("\nName another song title:");

  // scanf("%s", &b);

   scanf_s("%s", &b, 25);

   printf("\na = %s, b = %s\n", a, b);

}

1. Was the scanf_s() able to read the entire string or only the first word?

2. Was the gets_s() able to read the entire string or only the first word?

3. Did the gets_s() stop reading at the first space or the first return that was entered?

4. Did the puts() add a ‘\n’ at the end of the string that is printed?

5. Which function would you prefer to read in a string, scanf_s() or gets_s()?

1. Only the first word.

2. The entire string.

3. The first return that was entered.

4. Yes it did.

5. Of course gets()/gets_s().

2. Firstly, enter “Ooowee Babe” and then 2.40 for the following program. Show the output and answer the questions.

#include<stdio.h>

void main()

{

  // definition of structure

  struct Song

   {

        char Name[25];

        float Length;

   };

  // end of definition

  // variable declaration

  struct Song Title1;

   printf("The size of Title1 structure variable is %d bytes.\n",sizeof(Title1));

   puts("Name your favorite song title: ");

   gets_s(Title1.Name, 25);

   puts("How long is it?");

   scanf_s("%f", &Title1.Length);

   printf("\nYour song is ");

   puts(Title1.Name);

   printf("And it is %.2f min. long.\n", Title1.Length);

}

Just as the int and float are data types, struct Song is a new data type that we have defined.

1. What are the two known types used to define struct Song?

2. struct Song is defined with two members. What are their names?

3. Do the words char or float by themselves create new variables or allocate space in memory?

4. Since struct Song is also a new data type, do you think that it creates in itself a new variable?

5. Is a semicolon used at the end of the structure definition?

6. Since the definition of the structure doesn’t create a new variable, what is the name of the variable declared using the struct Song data type?

7. Title1 is a new variable that takes up space in memory. How many parts does it have? What are their names?

8. Show the contents of each member inside the box Title1.

9. An array is a collection of many items of the same data type, such as int or char. Similarly, a structure data type is a collection of many items. Do they have to be of the same data type?

10. When accessing a slot in an array, a set of brackets is used, such as a[2] = 0;. When we want to access a member of a structure, what do we use?

11. How would you have assigned the Length member of Title1 to 0?

12. How would you have assigned the name member of Title1 to “Mr. Moonlighting”?

---------------------------------------------------------------

1. char and float.

2. Name and Length.

3. They allocate space in memory.

4. Yes it creates in itself a new variable.

5. Yes.

6. Title1.

7. It has two parts named name and length.

8. ...

9. No. structure can have different data types.

10. We use a dot operator and the structure's member name.

11. Title1.Length = 0;

12. Title1.Name = “Mr. Moonlighting”.

3. In the following program example enter “Riders on the Storm” and 3.10 for the sample input data. Show the output and answer the questions.

#include<stdio.h>

#include<string.h>

void main()

{

  struct Song

   {

        char Name[25];

        float Length;

   };

  struct Song Title1, Title2;

   strcpy_s(Title2.Name, 25, "My Teardrops");

   Title2.Length = 2.35f;

   puts("Name your favorite song:");

   gets_s(Title1.Name, 25);

   puts("How long is it?");

   scanf_s("%f", &Title1.Length);

   printf("\nMy song is %s\n Your song is ", Title2.Name);

   puts(Title1.Name);

   printf("Yours is %.2f min. longer \n", Title1.Length - Title2.Length);

}

1. Can you print out both members of Title2 without specifying the member names as shown below? Does this work?

printf("%s %.2f\n", Title2);

2. Can you assign Title2 to Title1 without specifying their members as shown below? Does this work?

Title1 = Title2;

3.  Does the following code work? Why or why not?

Title1.Name = Title2.Name

1. No, we can't and this doesn't work. We need the name of the member.

2. Yes we can and it does work provided that they both have same structure as in this example. Here we assign the whole structure.

3. It doesn't work. We cannot assign the value of Title2.Name directly to Title1.Name but we can copy the value as the following code:

strcpy_s(Title1.Name, 25, Title2.Name);