difference between structure and union in C Language

October 10, 2013 , 19 Comments

In c language article we will see the difference between union and structure. Both are the user define datatype in c language. See the table which is mentioned below:
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1.The keyword  struct is used to define a structure
1. The keyword union is used to define a union.
2. When a variable is associated with a structure, the compiler allocates the memory for each member. The size of structure is greater than or equal to the sum of  sizes of its members. The smaller members may end with unused slack bytes.
2. When a variable is associated with a union, the  compiler allocates the  memory by considering the size of the largest memory. So, size of union is equal to the size of largest member.
3. Each member within a structure is assigned unique storage area of location.
3. Memory allocated is shared by individual members of union.
4. The address of each member will be in ascending order This indicates that memory for each member will start at different offset values.
4. The address is same for all the members of a union. This indicates that every member begins at the same offset value.
5 Altering the value of a member will not affect other members of the structure.
5. Altering the value of any of the member will alter other member values.
6. Individual member can be accessed at a time
6. Only one member can be accessed at a time.
7. Several members of a structure can initialize at once.
7. Only the first member of a union can be initialized.

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  1. Thanx its help for me at the exam time

  2. Thanks a lot ..............
    this is excellent difference between STRUCTURE and UNION.......

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  4. How we can multiply two no without using a*b opearation?

    1. use for loop and add addition of iteration like
      int sum=0;
      int a=5;

  5. Thanks lot
    I was searching for this.......

  6. great work .....appreciative

  7. How to swap 2 elments a&b with out using an 3rd element

    1. After entering a and b values...
      Use these set of instructions to swap two numbers..


      And then print a and b values.. They will be swapped

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