Union
Duration: 3 min
This video lesson is available to enrolled students.
Inside: a video lesson and guided study material.
Module outline
- English Comprehension: Comprehension / Reading Comprehension / Unseen Passages (Critical Reasoning) (Paragraph Questions), Reading Comprehension, Vocabulary, Idioms and Phrases, Narrative Sequencing, Critical Reasoning
- Reasoning and Aptitude: Series (Number and Letter Series) (Numerical Relations and Reasoning), Coding Decoding, Analogy, Non Verbal Reasoning (Spatial Aptitude) (Spatial Reasoning) (Visual Reasoning), Blood Relations, Directions (Direction Test), Ranking, Order and Sequence, Logical Sequence Of Words, Seating Arrangements, Puzzle Solving (Puzzles), Syllogisms, Deductive and Inductive Reasoning (Logical Deduction and Induction) (Prepositional Reasoning), Data Sufficiency, Selection Decision Table (Decision Making), Calendar, Clock, Cubes & Dices, Data Arrangement, Venn Diagram, Analytical Reasoning (Counting Figures Reasoning), Number System, HCF LCM, Percentage, Ratio and Proportion (Ratios), Average, Profit and Loss, Simple Interest and Compound Interest, Speed Time and Distance, Mensuration and Geometry, Arithmetic, Mixture and Alligation, Age Problems, Data Interpretation, Alphabet and Word Tests, Numerical Reasoning, Number System, Averages, Mixtures and Alligation, Percentages, Series Completion, Analogy and Classification, Patterns in Two-Dimensional Figures, Coding and Decoding, Mathematical Operations, Direction Sense, Logical Deduction and Induction, Simplification and Approximation, Assembling and Grouping of Shapes, Transformation of Shapes, Three-Dimensional Patterns and Visualization, Cubes and Dice, Algebra, Traverse Surveying, Clocks and Calendars, Order, Ranking and Sequence, Constraint Puzzles, Syllogisms and Venn Diagrams, Ratio and Proportion, Mensuration, Permutations and Combinations, Project Monitoring, Resources and Safety, Profit, Loss and Discount, Sequences and Series, Powers, Surds and Logarithms, Subject-Verb Agreement, Sentence Completion, Geometry, Probability, Trigonometry, Measurement and Quantity Take-Off, Statistics, Data Sufficiency, Blood Relations, Speed, Time and Distance, Time and Work, Data Interpretation, Sequence and Series (Series), Algebra, Permutation and Combination, Combinatorics
- General Awareness: Physics, Chemistry, Biology, Geography, History, Polity, Indian Economy
- Computer Fundamentals: Basics of COA, Number System, Number Representation, Semiconductor Memories and Programmable Logic, Timing, Hazards and Testing, Processor Organization and Instructions, Number Systems and Codes, Combinational Logic Design, Combinational Logic Circuits, Number Systems and Codes
- Operating System: Introduction to OS, Unix OS, Linux OS
- C Programming: C Fundamentals, Control Flow, Functions, Arrays & Pointers, Storage Classes, Structures & Enums, DMA, Macros, Scoping & File Handling
- OOPS with C++ & Java: OOPS with C++, Java
- Database Management System: Basics of DBMS, SQL
- MS Office: MS Office Applications
- Internet & Web Technologies: Website, Browser & Services, Internet Fundamentals, Web Design & Development, Protocols & Services
AI summary & chapters
AI Summary
An AI-generated summary of this video lecture.
This lecture introduces the Union data structure in C programming as a user-defined datatype that groups variables of different types while sharing the same memory location. The instructor explains that unlike structures, only one member can hold a valid value at any given time because all members occupy the same memory space. The total size of a union is determined by its largest member, illustrated with an example where the character array str[20] dictates a total size of 20 bytes. The lesson demonstrates this behavior through code examples showing how assigning an integer value to one member and then a float to another overwrites the previous data due to shared memory allocation.
Chapters
0:00 – 2:00 00:00-02:00
The instructor defines a Union in C as a user-defined datatype that groups variables of different data types but shares the same memory location. On-screen text explicitly states 'Groups variables of different datatypes, but shares the same memory location' and 'Only one member can hold a value at a time.' The code snippet `union Data {int i; float f; char str[20];};` is displayed, followed by the declaration `union Data d1; //Total size = 20 bytes.` The instructor annotates member sizes (4B for int, 8B for float) and underlines key phrases to emphasize the shared memory concept. The example `d1.i = 10;` is shown to initialize the union.
2:00 – 3:14 02:00-03:14
The lesson continues by demonstrating the overwrite behavior inherent to unions. The instructor shows how assigning a float value, such as `d1.f = 22.5;`, overwrites the previously stored integer value in the same memory space. Visual annotations highlight that the total size remains 20 bytes, determined by the largest member `char str[20]`. The instructor draws arrows to show overlapping memory usage for int, float, and char members. The final code snippet `printf("%d", d1.i);` is presented to illustrate how reading the integer member after a float assignment yields undefined or garbage values due to the shared memory location.
The video provides a foundational understanding of C unions by contrasting them with structures through memory allocation principles. The core concept is that union members share the same physical address, meaning writing to one member invalidates previous values in other members. The size calculation is strictly based on the largest member, ensuring sufficient space for any single type within the union. This behavior is critical for memory-efficient programming where only one data type needs to be stored at a time. The examples clearly show the practical implications of this design, such as data overwriting when switching between int and float assignments within the same union variable.