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Which of the following line(s) will cause a compilation error?

Qualcomm technical mcq question, verified with a worked answer. Free to practise - no sign-up.

struct book
{
    int b1;
    unsigned float b2;        //Line 1
    !b2;
    
    union notebook
    {
        static int n1;        //Line 2
        short int n2;         //Line 3
    }n;
    
    printf("%d", sizeof(b) + sizeof(n));  //Line 4
    return 0;
}

Which of the following line(s) will cause a compilation error?

Show answer & explanation

Answer: C. Line 1 and Line 2

Line 1 is invalid because unsigned float is not a valid type qualifier combination in C (only unsigned applies to integral types, not floating-point). Line 2 is invalid because static cannot be used for members inside a union or struct—it only applies to file scope or function scope variables. Line 3 is valid C syntax. Line 4 would fail for a different reason (undefined identifiers b and n in a struct definition context), but the primary compilation errors occur at Lines 1 and 2.

Step-by-step Derivation:
Step-by-step analysis of each line:

Line 1: unsigned float b2; — COMPILATION ERROR
- In C, unsigned is a type qualifier for integral types (char, short, int, long)
- Floating-point types (float, double) do not support the unsigned qualifier
- This violates C type rules and will cause a compile-time error
Line 2: static int n1; — COMPILATION ERROR
- The static storage class specifier cannot be used for struct or union members
- static is only valid for file-scope variables, function-scope variables, or function declarations
- Members inside a struct/union must use no storage class or alignment specifiers like _Alignas
- This causes a compilation error
Line 3: short int n2; — VALID
- This is syntactically correct; short int is a valid integral type for union members
Line 4: printf("%d", sizeof(b) + sizeof(n)); — Would be an error for different reasons
- Even if Lines 1–2 were fixed, this line has issues: b and n are not defined outside the struct scope
- However, the question asks specifically about compilation errors, and Lines 1 and 2 are the primary syntax violations

Answer: C) Line 1 and Line 2