# C Programming Exercises, Practice, Solution : Queue

## C Queue [13 exercises with solution]

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From Wikipedia -
In computer science, a queue is a collection of entities that are maintained in a sequence and can be modified by the addition of entities at one end of the sequence and the removal of entities from the other end of the sequence. By convention, the end of the sequence at which elements are added is called the back, tail, or rear of the queue, and the end at which elements are removed is called the head or front of the queue, analogously to the words used when people line up to wait for goods or services.

1. Write a C program to implement a queue using an array. Programs should contain functions for inserting elements into the queue, displaying queue elements, and checking whether the queue is empty or not. Go to the editor
Expected Output:

Initialize a queue!
Check the queue is empty or not? Yes

Insert some elements into the queue:
Queue elements are: 1 2 3

Insert another element into the queue:
Queue elements are: 1 2 3 4

Check the queue is empty or not? No

Click me to see the solution

2. Write a C program to implement a queue using an array. Create a function that removes an element from the queue. Go to the editor
Expected Output:

Initialize a queue!
Insert some elements into the queue:
Queue elements are: 1 2 3

Delete an element from the said queue:
Queue elements are: 2 3

Insert another element into the queue:
Queue elements are: 2 3 4

Click me to see the solution

3. Write a C program to implement a queue using a linked list. Programs should contain functions for inserting elements into the queue, displaying queue elements, and checking whether the queue is empty or not. Go to the editor
Expected Output:

Initialize a queue!
Check the queue is empty or not? Yes

Insert some elements into the queue:
1 2 3

Insert another element into the queue:
1 2 3 4

Check the queue is empty or not? No

Click me to see the solution

4. Write a C program to implement a queue using an array. Create a function that removes an element from the queue. Go to the editor
Expected Output:

Initialize a queue!
Check the queue is empty or not? Yes

Insert some elements into the queue:
1 2 3

Insert another element into the queue:
1 2 3 4

Check the queue is empty or not? No

Click me to see the solution

5. Write a C program to count the number of elements in a queue. Go to the editor
Expected Output:

Initialize a queue!
Check the queue is empty or not? Yes
Number of elements in queue: 0

Insert some elements into the queue:
Queue elements are: 1 2 3
Number of elements in queue: 3

Delete two elements from the said queue:
Queue elements are: 3
Number of elements in queue: 1

Insert another element into the queue:
Queue elements are: 3 4
Number of elements in the queue: 2

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6. Write a C program to reverse the elements of a queue. Go to the editor
Expected Output:

Queue elements are:
1 2 3 4 5
Reverse Queue, elements are:
5 4 3 2 1
Add two elements to the said queue:
Queue elements are:
5 4 3 2 1 100 200
Reverse Queue, elements are:
200 100 1 2 3 4 5

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7. Write a C program to calculate the sum of the elements in a queue. Go to the editor
Expected Output:

Queue elements are: 1 2 3 4 5
Sum of the elements in the queue is: 15

Remove 2 elements from the said queue:
Queue elements are: 3 4 5
Sum of the elements in the queue is: 12

Insert 3 more elements:
Queue elements are: 3 4 5 300 400 500
Sum of the elements in the queue is: 1212

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8. Write a C program to compute the average value of the elements in a queue. Go to the editor
Expected Output:

Queue elements are: 1 2 3 4 5
Average of the elements in the queue is: 3.000000

Remove 2 elements from the said queue:
Queue elements are: 3 4 5
Average of the elements in the queue is: 4.000000

Insert 3 more elements:
Queue elements are: 3 4 5 300 427 519
Average of the elements in the queue is: 209.666672

Click me to see the solution

9. Write a C program to find the maximum element in a queue. Go to the editor
Expected Output:

Queue elements are: 1 2 3 4 5
Maximum value in the queue is: 5

Remove 2 elements from the said queue:
Queue elements are: 3 4 5
Maximum value in the queue is: 5

Insert 3 more elements:
Queue elements are: 3 4 5 600 427 519
Maximum value in the queue is: 600

Click me to see the solution

10. Write a C program to find the minimum element in a queue. Go to the editor
Expected Output:

Queue elements are: 1 2 3 4 5
Minimum value in the queue is: 1

Remove 2 elements from the said queue:
Queue elements are: 3 4 5
Minimum value in the queue is: 3

Insert 3 more elements:
Queue elements are: 3 4 5 600 -427 519
Minimum  value in the queue is: -427

Click me to see the solution

11. Write a C program to delete the nth element of a queue. Go to the editor
Firstly, this code checks if the queue is empty or if the position to delete is invalid. If the position is valid, it deletes the first n-1 elements, then deletes the nth element by calling the dequeue() function
Expected Output:

Insert some elements into the queue:
Queue elements are: 1 2 3 4 5

Delete the 7th element of the said queue:
Error: Invalid position

Delete the 3rd element of the said queue:
Queue elements are: 4 5

Click me to see the solution

12. Write a C program to sort the elements of a queue in ascending order. Go to the editor
Expected Output:

Input some elements into the queue:
Elements of the queue:
4 2 7 5 1

Sort the said queue:
Elements of the sorted queue in ascending order:
1 2 4 5 7

Input two more elements into the queue:
Elements of the queue:
1 2 4 5 7 -1 3

Sort the said queue:
Elements of the sorted queue in ascending order:
-1 1 2 3 4 5 7

Click me to see the solution

13. Write a C program to find the median of the elements in a queue. Go to the editor
From Wikipedia,
In statistics and probability theory, the median is the value separating the higher half from the lower half of a data sample, a population, or a probability distribution.
The median of a finite list of numbers is the "middle" number, when those numbers are listed in order from smallest to greatest.
If the data set has an odd number of observations, the middle one is selected. For example, the following list of seven numbers,
1, 3, 3, 6, 7, 8, 9
has the median of 6, which is the fourth value.
If the data set has an even number of observations, there is no distinct middle value and the median is usually defined to be the arithmetic mean of the two middle values. For example, this data set of 8 numbers1, 2, 3, 4, 5, 6, 8, 9 has a median value of 4.5, that is (4+5)/2 . (In more technical terms, this interprets the median as the fully trimmed mid-range).
Expected Output:

Input some elements into a queue:
Queue elements are:
1 2 3 4 5
The median of the elements in the queue is 3.000000

Input one more element:
Queue elements are:
1 2 3 4 5 6
The median of the elements in the queue is 3.500000

Click me to see the solution

C Programming Code Editor:

More to Come !

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## C Programming: Tips of the Day

C Programming - How do you pass a function as a parameter in C?

Declaration

A prototype for a function which takes a function parameter looks like the following:

void func ( void (*f)(int) );

This states that the parameter f will be a pointer to a function which has a void return type and which takes a single int parameter. The following function (print) is an example of a function which could be passed to func as a parameter because it is the proper type:

void print ( int x ) {
printf("%d\n", x);
}

Function Call

When calling a function with a function parameter, the value passed must be a pointer to a function. Use the function's name (without parentheses) for this:

func(print);

would call func, passing the print function to it.

Function Body

As with any parameter, func can now use the parameter's name in the function body to access the value of the parameter. Let's say that func will apply the function it is passed to the numbers 0-4. Consider, first, what the loop would look like to call print directly:

for ( int ctr = 0 ; ctr < 5 ; ctr++ ) {
print(ctr);
}

Since func's parameter declaration says that f is the name for a pointer to the desired function, we recall first that if f is a pointer then *f is the thing that f points to (i.e. the function print in this case). As a result, just replace every occurrence of print in the loop above with *f:

void func ( void (*f)(int) ) {
for ( int ctr = 0 ; ctr < 5 ; ctr++ ) {
(*f)(ctr);
}
}

Ref : https://bit.ly/3skw9Um