Answer» - STRUCT: In C, a structure is a user-defined data type that allows you to combine data objects of various types. A record is represented by a structure.
Syntax: struct structureName { member DEFINITION; member definition; ... member definition; }; - union: In C, a union is a unique data type that allows you to store many data types in the same memory region. A union can have numerous members, but only ONE of them can have a value at any given time. Unions are a useful approach to reuse the same memory space for numerous purposes.
Syntax: union unionName { member definition; member definition; ... member definition; };The following table illustrates the differences between struct and union: | struct | union |
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| A structure is defined using the struct keyword. | Union is defined by the keyword union. | | The compiler allocates memory to each VARIABLE member when the variables are declared in a structure. The total size of each data member determines the size of a structure. | When a variable is declared in a union, the compiler allocates memory to the variable member with the largest size. A union's size is determined by the size of its largest data member. | | Changing a variable's value has no effect on other variables present in the struct. | Changing the value of one variable member will have an impact on the other variables present in the union. | | Each variable's member has its own memory area. | Members of a variable share the memory space of the variable with the largest size. | | Multiple variables in a structure can be initialised at the same time. | Only the first data member of a union can be initialised. | | At any point in the program, all variable members store some value. | At any given point in the program, exactly one data member stores a value. | | It's used to keep track of various data types' values. | It's used to save one value at a time from a variety of data types. | | It provides for the simultaneous access and retrieval of any data member. | It lets you access and retrieves individual data members at a time. |
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