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Just like a human mind, computers too need to assign memory to a specific location. That is why the concept of memory allocation comes into being. 

Memory allocation simply means that you are assigning a specific location or space to the program code in your computer. However, in C there are two major types or kinds of memory allocations ; Static memory allocation and dynamic memory allocation. 

Though, both the terms are used to allocate memory, there are key note differences between them. But before throwing light on the differences between static and dynamic memory, let’s get into their detailing.

Types of Memory allocation in C

Before directly jumping to the difference between static and dynamic memory allocation, it is essential to know about both methods in detail.

Static memory allocation

Static memory is also called compile-time memory allocation and belongs to the stack memory category. In static memory allocation, the space you allot to a certain code is in a fixed size. Each variable in the C code is given a fixed space and In this case, the static variables are allocated permanently in the memory with static memory allocation. 

The Static memory allocation method uses the stack memory technique to allot memory to variables during the compilation process. Once memory allocation is done, you can not reuse or resize the memory space. Static memory is widely used in arrays. 

Advantages of Static memory allocation

• It is highly useful in cases where you wish to allocate memory before time like in arrays
• This memory allocation method is highly convenient to use and can easily be learned
• Variable memories will not change throughout the program
• Execution time is less making this process faster and more relevant. 

Dynamic memory allocation

Dynamic memory is also called run-time memory allocation because, in this type of memory allocation, memory is allocated to variables at the time of execution of the code or data. Memory is allotted to the program during the first time any code runs. Dynamic memory allocation provides space and size accurately at the runtime which saves the space in the main memory.

 You can assign dynamic variables in C with four different functions. These functions are:

• Malloc function
• Realloc Function
• Calloc Function
• Free() 

This memory allocation is widely used in linked lists as it uses heap memory to allocate memory for dynamic variables. 

Advantages of Dynamic memory allocation

• The memory is allocated at the execution 
• Since, memory space is not fixed and hence there is the least wastage of space
• The space can be resized and then reused as per the requirement 
• It provides higher efficiency as compared to static memory allocation. 

You can also use dynamic memory allocation when you need to manage an unbounded knapsack. 

The knapsack problem is just like a bag is provided to you to keep some things to keep in it. The main idea is to increase the benefit while not increasing capacity. This is based on Dynamic Programming. Unbound Knapsack is the extension or more advanced version of the basic Knapsack Problem. The major difference is there that we can use Unbounded Knapsack an infinite number of times ulike 0-1 Knapsack.

Types of Approaches:- 

Brute Force Approach

If we’re given a list of objects together with their weights and profits and asked to calculate the largest profit conceivable, the first thing that comes to mind is the brute-force method. Here, we’ll attempt all conceivable combinations of things, keeping track of the earnings we make in each, and then computing the maximum of those profits as our response.

Dynamic Programming Approach

Dynamic Programming is the way to tackle this problem, Similar to classical Knapsack. The big difference here is that the 1-D array is to be used instead of 2-D array in the classical Knapsack. Well, this happens as we have an infinite supply of all the available elements.

So, no need to keep a track.

Difference between Static and Dynamic memory allocation

Following are the usual parameters on which you can easily differentiate between static and dynamic memory allocation. 

• Based on Nature

Static memory allocation is fixed in nature which means you can not change Or resize the allocated space at any time in the code. Whereas Dynamic memory allocation can be changed at any instant according to the variable and its value. This is one of the major differences between static and dynamic memory allocation. 

• Based on Time of allotment

In dynamic memory, allocation memory is allocated at the runtime or simply at the execution time of a particular code.However, in static memory allocation, the memory is allocated to a variable as soon as the code is compiled. 

• Size of memory

In dynamic memory allocation, there is not a fixed value of memory allocated to the dynamic variable and thus, it can be reused again and again as per the requirement. In static memory allocation, once the memory is allocated you will not be able to change it or reuse it as the memory is allocated permanently.

• Based on the period

In static memory allocation, the memory is allocated starting from the beginning of the code till the end. Whereas in dynamic memory allocation, memory can easily be allocated at any instant throughout the program.

• Based on command

 To allot a dynamic memory to a variable you will have to use functions like realloc(), free(), calloc(), and malloc() with the variable. Static memory can easily be allocated by using the static() command in C.

• Based on memory area used

 Static memory uses stack memory for storing and managing the variables. On the other hand, the dynamic memory allocation uses heap memory for storing and managing the dynamic variables.

• Based on the Period for execution

 Static memory allocation is done at the compiling stage and thus requires lesser time as compared to dynamic memory allocation. Dynamic memory allocation requires much time for execution and the whole process of this allocation is quite slower than the static memory allocation process. This is one of the most important differences between static and dynamic memory allocation.

• Based on efficiency

 The allocation scheme of dynamic memory is highly efficient due to several reasons. This memory allocation is more efficient than the other type of static memory allocation program or scheme is slightly less efficient than the dynamic memory allocation scheme

• Based on implementation 

Dynamic memory allocation is a complicated process for memory allocation in C. It is complex and requires a good grasp of the knowledge and the language. 

The static memory allocation process is easy to complete or implement with the help of simple functions or coding.

• Based on Functions for C

Dynamic memory allocation can be done with four different functions i.e. Malloc, calloc, free, and really. You can use these functions to allot dynamic memory to a certain variable while developing a code in C. For static memory allocation in the case of a variable, all you need to do is add the word “static” before your variable and your variable will be allotted static memory. 

• Based on Application 

The dynamic memory allocation is widely used in linked lists. Static memory allocation is used in an array during coding in C.

Conclusion

Static and dynamic memory allocation comes with different advantages and disadvantages of its own. You can select any method of memory allocation based on your purpose, knowledge, and requirement from a program. 

Once you understand all the primary components of the difference between static and dynamic memory allocation, it becomes easier to implement them accordingly. Make sure you learn about both the memory allocation techniques individually to make an informed decision.