Question

C supports user-defined data types. Explain the following data type features of the C language and provide a sample for each in C code (2 marks each): . Renaming of data-types • Enumerations • Structures • Unions • Bit-fields

Answer 1

[1] Renaming data types

Instead of using the predefined keywords for a certain type of data, we can customize its name according to the requirement of the program. It is achieved using the typedef keyword.

Eg.         typedef int number;

Now all integer type variable can be declared using number x instead of int x.

[2] Enumeration

An enumeration is a data type that contains integral constants. In other words, a variable declared as enum type can only hold a limited amount of values as specified during declaration. The keyword enum is used.

Eg.         enum week {Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday};

              enum week x;

Now, x can only hold values which correspond to the seven days of the week.

[3] Structures

A structure is a user-defined data type that comprises of (or encapsulates) multiple data types and can be used as a singular entity. The struct keyword is used.

Eg.         struct struct_name{

              int x;

              char y;

} var1, var2;

Here, var1 and var2 are variables of type struct_name and can hold one integer and one character each.

[4] Union

A union allows us to reuse the same memory location to store different types of data. It can have multiple data members but only one can hold a value a time. The union keyword is used to declare the union and its members are accessed using the . (dot) operator.

Eg.         union union_name {

              int i;

              float f;

}var1;

Now var1 can either hold I or f but not both. If we assign multiple values, only the latest will be stored in memory.

[5] Bit-fields

Bit-fields are used to specify the maximum number of bits that can be occupied by a given variable. These are used to make a program more memory efficient.

Eg.         int x:3;

Here x can only hold values that can be represented using three bits, ie, 000 to 111 (0 to 7 in decimal).