Program for array based implementaion of queue in C

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This is my program to implement queue using ARRAY, this code is not working fine for all
operations except first deque operation.When i am calling first dequeue than it should show me output 12 but it is not showing
i am new to programming can anyone help me

the outputof this program is as shown below

What I have tried:

#include<stdio.h>
#include<stdlib.h>
struct queue{
    int capacity;
    int rear;
    int front;
    int *array;
};
struct queue* createqueue(int capacity){
    struct queue* nque=(struct queue*)malloc(sizeof(struct queue));
    nque->capacity=capacity;
    nque->front=-1;
    nque->rear=-1;
    nque->array=(int*)malloc(sizeof(int)*capacity);
    return nque;

}
int isempty(struct queue* amp){
    return(amp->front==-1&&->rear==-1);
}
int  isfull(struct queue* amp){
    return (((amp->rear)+1)%(amp->capacity)==amp->front);

}
void enqueue(struct queue* amp,int x)
{
    if(isfull(amp))
        return;
    else if(isempty(amp))
    {
        amp->rear=0;
        amp->front=0;
    }
    else
    {
        amp->rear=(amp->rear+1)%(amp->capacity);

    }
    amp->array[amp->rear]=x;
}
int dequeue(struct queue* amp)
{
    if(isempty(amp))
        return -1;
    else if(amp->front==amp->rear)
    {
        amp->front=-1;
        amp->rear=-1;
        return(amp->array[amp->front]);
    }
    else
    {
        amp->front=((amp->front)+1)%(amp->capacity);
        return(amp->array[amp->front]);
    }
}
int main(){
    struct queue* queue=createqueue(10);
    enqueue(queue,12);
    enqueue(queue,136);
    enqueue(queue,14);
    enqueue(queue,13);
    enqueue(queue,16);

    printf("\n%d",dequeue(queue));
    printf("\n%d",dequeue(queue));
    printf("\n%d",dequeue(queue));

    printf("\n%d",dequeue(queue));
    printf("\n%d",dequeue(queue));
    printf("\n%d",dequeue(queue));
    printf("\n%d",dequeue(queue));



}

Posted 15-Aug-18 2:46am

kavinderrana121

Updated 15-Aug-18 3:34am

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OriginalGriff · Answer 1 · 2018-08-15T03:11:00

Compiling does not mean your code is right! :laugh:
Think of the development process as writing an email: compiling successfully means that you wrote the email in the right language - English, rather than German for example - not that the email contained the message you wanted to send.

So now you enter the second stage of development (in reality it's the fourth or fifth, but you'll come to the earlier stages later): Testing and Debugging.

Start by looking at what it does do, and how that differs from what you wanted. This is important, because it give you information as to why it's doing it. For example, if a program is intended to let the user enter a number and it doubles it and prints the answer, then if the input / output was like this:

Input   Expected output    Actual output
  1            2                 1
  2            4                 4
  3            6                 9
  4            8                16

Then it's fairly obvious that the problem is with the bit which doubles it - it's not adding itself to itself, or multiplying it by 2, it's multiplying it by itself and returning the square of the input.
So with that, you can look at the code and it's obvious that it's somewhere here:

C#

int Double(int value)
   {
   return value * value;
   }

Once you have an idea what might be going wrong, start using the debugger to find out why. Put a breakpoint on the first line of the main method, and run your app. When it reaches the breakpoint, the debugger will stop, and hand control over to you. You can now run your code line-by-line (called "single stepping") and look at (or even change) variable contents as necessary (heck, you can even change the code and try again if you need to).
Think about what each line in the code should do before you execute it, and compare that to what it actually did when you use the "Step over" button to execute each line in turn. Did it do what you expect? If so, move on to the next line.
If not, why not? How does it differ?

Start by looking at the actual queue before an after each enqueue operation: do you end up with the queue looking exactly as it should? Do not assume it works: check it before and after each operation.
When you have enqueued everything correctly, step into your dequeue function and look closely at what is going on.

Hopefully, that should help you locate which part of that code has a problem, and what the problem is.
This is a skill, and it's one which is well worth developing as it helps you in the real world as well as in development. And like all skills, it only improves by use!

Patrice T · Answer 2 · 2018-08-15T03:28:00

Quote:
When i am calling first dequeue than it should show me output 12 but it is not showing

You are obviously messing with front and end.
Advice: Take a sheet of paper and a pencil, simulate the queue behavior, don't forget front and rear, compare with what your code is doing.
-----
Your code do not behave the way you expect, or you don't understand why !

There is an almost universal solution: Run your code on debugger step by step, inspect variables.
The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don't know what your cpde is supposed to do, it don't find bugs, it just help you to by showing you what is going on. When the code don't do what is expected, you are close to a bug.
To see what your code is doing: Just set a breakpoint and see your code performing, the debugger allow you to execute lines 1 by 1 and to inspect variables as it execute.

The downside of this solution:
- It is a DIY, you are the one tracking the problem and finding its roots, which lead to the solution.
The upside of this solution:
- It is also a great learning tool because it show you reality and you can see which expectation match reality.

secondary effects
- Your will be proud of finding bugs yourself.
- Your learning skills will improve.

You should find pretty quickly what is wrong.

Debugger - Wikipedia, the free encyclopedia[^]

Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]
Basic Debugging with Visual Studio 2010 - YouTube[^]
1.11 — Debugging your program (stepping and breakpoints) | Learn C++[^]
The debugger is here to only show you what your code is doing and your task is to compare with what it should do.

Program for array based implementaion of queue in C

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