C unions — what is printed after storing a float in a union and reading it back?\n\n#include<stdio.h>\n#include<stdlib.h>\n\nint main()\n{\n union test\n {\n int i;\n float f;\n char c;\n };\n union test *t = (union test *) malloc(sizeof(union test));\n t->f = 10.10f;\n printf("%f", t->f);\n return 0;\n}\n\nAssume malloc succeeds.

Introduction / Context:
This question focuses on unions in C and accessing the same member that was most recently written. It checks whether learners understand that reading back the same active member yields the stored value, subject to normal floating-point formatting in printf.

Given Data / Assumptions:

• t points to a valid union test object.
• t->f is assigned 10.10f.
• printf uses "%f" to print a float (promoted to double on call).

Concept / Approach:
If you write to one member of a union and then read the same member, you get the stored value. Using a different member without writing it is not meaningful. printf("%f") will display the value with default precision (typically 6 places after the decimal), so 10.10f prints as 10.100000 by default.

Step-by-Step Solution:

Verification / Alternative check:
Formatting can be changed using "%.2f" to print "10.10". With the default "%f", expect "10.100000".

Why Other Options Are Wrong:

• 10: Not the default "%f" precision.
• Garbage value: Would occur only if reading a different member than written.
• Error: The code is valid if malloc succeeds.

Common Pitfalls:
Assuming unions always cause aliasing issues; here the same member is consistently used, which is fine.

Final Answer:
10.100000