Which of the following correctly declares a structure?

Question

BlackTom AI · Accepted Answer

Here is a step-by-step analysis of each answer option to understand why one fits the syntax rules for declaring a structure, while the others do not.
Option 1: 'struct { int x; float y;};' This option uses the keyword struct followed by an anonymous struct body containing two members, int x and float y, and ends with a semicolon. In C and C++, declaring a struct this way defines an unnamed struct type. While some compilers may require a declarator to define an actual object, this form is recognized as a valid struct-type declaration in many contexts, and it matches the pattern of declaring a struct type (even though it lacks a tag or a variable name). Comparatively, the absence of a tag or name is the key feature here, and the syntax aligns with how anonymous structs can be introduced.
Option 2: 'structure abc {int x;};' This uses the word 'structure' instead of the correct keyword 'struct' (in C and C++). Since the language grammar does not recognize 'structure' as a type-declaration keyword, this is a syntax error. The trailing semicolon does not rescue it because the initial token is invalid.
Option 3: 'struct abc int x;' Here, the declaration attempts to combine a struct tag with a declarator in a single line but omits the required punctuation. The correct form to declare a struct type with a tag would be something like 'struct abc { int x; };' or 'struct abc { int x; } obj;'. As written, there is no valid declarator or body following the tag, so this is not valid syntax.
Option 4: 'struct abc ={int x;};' This mixes a struct tag 'abc' with an initializer-like syntax inside the declaration, which is not valid C/C++ syntax for struct declarations. Assigning a brace-enclosed initializer directly to a struct tag in this context is not permitted, and the overall structure fails to conform to the language grammar for type declarations.
In summary, Option 1 presents a structurally correct form for declaring an anonymous struct type, while Options 2–4 violate the language's keywords, required punctuation, or the well-formedness rules for struct declarations.

CEA3201 17984 MAIN - Computer Programming for Engineers Final exam CEA 3201 theory

Which of the following correctly declares a structure?

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