C program for Evaluating a Postfix Expression

The Algorithm for Evaluating a Postfix Expression  is given here

Program:

#include<stdio.h>
#include<ctype.h>
#include<stdlib.h>
#define SIZE 40
int stack[SIZE];
int top=-1;

void push(int n)
{
    if(top==SIZE-1)
    {
        printf("Stack is full\n");
        return;
    }
    else
    {
        top=top+1;
        stack[top]=n;
        printf("Pushed element is %d\n",n);
    }
}

int pop()
{
    int n;
    if(top==-1)
    {
        printf("Stack is empty\n");
        return;
    }
    else
    {
        n=stack[top];
        top=top-1;
        printf("The poped element is %d\n",n);
        return(n);
    }
}

int evaluate(int op1, int op2,char ch)
{
    printf("op1=%d op2=%d ch=%c\n",op1,op2,ch);
    int n;
    if (op1<op2)
    {
        n=op1;
        op1=op2;
        op2=n;
        }
    if(ch=='+')
        n=op1+op2;
    else if(ch=='-')
        n=op1-op2;
    else if(ch=='*')
        n=op1*op2;
    else if(ch=='/')
        n=op1/op2;
    else if(ch=='%')
        n=op1%op2;
    else
    {
        printf("The operator is not identified\n");
        exit(0);
    }
    printf("n=%d\n",n);
    return(n);
}

int main()
{
      char str[50],ch,ch1;
      int i=0,n,op1,op2;

      printf("Enter the Postfix string\n");
      scanf("%s",str);
      ch=str[i];
      while(ch!='\0')
      {
        printf("The char is=%c\n",ch);
           //if(ch=='1' || ch=='2' || ch=='3' || ch=='4' || ch=='5')//
           if(isdigit(ch))
           {
                n=ch-'0';
                push(n);
           }
           else
           {
                op1=pop();
                op2=pop();
                n=evaluate(op1,op2,ch);
                push(n);
           }
           ch=str[++i];
      }
      printf("The value of the arithmetic expression is=%d\n",pop());
      return;
}

C Programs Based on Queue

Algorithm 1Write an algorithm for inserting an element in to the queue using array
Solution:
    Let Q be the array of specified size, SIZE

1. Initialize front=0,rear=-1
2. Input the value to be inserted and assign to variable "data"
3. If (rear > = SIZE)
         (a) Display "Queue Overflow"
         (b) Exit.
4. Else
         (a) rear=rear+1;
5. Q[rear]=data;
6. Exit

Algorithm 2: Write an algorithm for deleting an element from the queue using array
Solution
    Let Q be the array of specified size,SIZE

1. if (rear < front )
       (a) front=0,rear=-1
       (b) Display "The queue is empty"
       (c) Exit
2. else
       (a) Data=Q[front]
       (b) front=front+1;
3. Exit

C Programs Based on Stack

Program 1: Write a C program to implement stack operations push and pop using array.

Program 2: Write a C program to implement stack operations push and pop using Linked List.

Program 3:Design an algorithm,using a stack to read five characters from a keyboard and display them in reverse order.

Program 4:Design an algorithm,using a stack,which will convert a decimal number to binary.

Program 5:Design an algorithm using a stack,which will test whether an input string is palindromic or not

Program 6:Write a C function to copy one stack to another assuming the stack is implemented using array

Program 7:Write a C function to copy one stack to another assuming the stack is implemented using Linked list

C Programs based on LInked List

Sample Program 1:
Simple linear linked list constructed in c.Adding 10 elements into the list and print them
Program

#include "stdio.h"
#include "stdlib.h"

struct Node
{
   //each node contains a data and a pointer to the next node in the list
   int data;
   struct Node *next;
};

typedef struct Node node;

int main()
{
    node *newnode,*head,*first;
    int i;
    head=NULL;
    first=NULL;

    //Inserting 10 nodes in a list
    for(i=1;i<=10;i++)
    {
       newnode=(node*)malloc(sizeof(node));
       newnode->data=i;
       newnode->next=NULL;
  
       if(head==NULL)
       {
          head=newnode;
          first=newnode; //To point the first node in the list
        }
        head->next=newnode;
        head=newnode;
    }
     //Print the nodes in the list
     newnode=first;
     while(newnode)
     {
          printf("%d\t",newnode->data);
          newnode=newnode->next;
     }
}


Output:
1 2 3 4 5 6 7 8 9 10


Sample Program 2
Write a C program to perform the basic operation like insertion,deletion,display in a singly linked list.
solution
#include<stdio.h>
#include<stdlib.h>

void Insert_list(int);
void Insert_pos(int,int);
void delete_list(int);
void display(void);
void search(int);

struct Node
{
    int data;
    struct Node *next;
};

typedef struct Node node;
node *head=NULL,*curr=NULL;

int main()
{
    int ch,n,m;
    do
    {
        printf("ENter your choice\n1.Insert end of list\n2.Insert at position\n3.Delete\n4.Search\n5.Display\n6.Exit\n");
        scanf("%d",&ch);
        switch(ch)
        {
            case 1:
                    printf("Enter the data to insert\n");
                    scanf("%d",&n);
                    Insert_list(n);
                    break;
            case 2:
                    printf("Enter the data to insert\n");
                    scanf("%d",&n);
                    printf("Enter the position after the data is insert\n");
                    scanf("%d",&m);
                    Insert_pos(n,m);
                    break;
            case 3:
                    printf("Enter the data item to be delete\n");
                    scanf("%d",&n);
                    delete_list(n);
                    break;
            case 4:
                    printf("Enter the data item to be search\n");
                    scanf("%d",&n);
                    search(n);
                    break;
            case 5:
                    display();
                    break;
            case 6:
                    exit(0);
            default:
                    printf("Enter a valid digit\n");
                    break;
        }
    }while(ch>=1 && ch<=6);
}
void Insert_list(int n)
{
    node *newnode;
    //creating a new node with data n
    newnode=(node *)malloc(sizeof(node));
    newnode->data=n;
    newnode->next=NULL;
    //check the head node. If head is NULL then the list is empty
    //insert this node as the head node
    if(head==NULL)
    {
        head=newnode;
        curr=head;
    }
    else
    {
        //curr is the pointer pointing the last node of the list
        curr->next=newnode;
        curr=newnode;
    }
}

void Insert_pos(int n,int pos)
{
    node *nnode,*newnode;
    int i;
    if(head==NULL)
    {
        printf("The list is empty\n");
        return;
    }
    //assigning a temporary pointer nnode to point the head node
    nnode=head;
    //finding the position in the list
    for(i=0;i<pos-1;i++)
    {
        nnode=nnode->next;
        if(nnode==NULL) //reached end of list
        {
            printf("There are less than %d nodes in the list\n",pos);
            return;
        }
    }
    //found the position to insert
    //create a newnode with given data n
    newnode=(node *)malloc(sizeof(node));
    newnode->data=n;
    newnode->next=NULL;
    //inserting after the position
    newnode->next=nnode->next;
    nnode->next=newnode;
    printf("Node with value %d inserted after %d position\n",n,pos);
    return;
}

void delete_list(int n)
{
//Search the given item in the list if it is present delete or print a message
    node *nnode,*temp;
    if(head==NULL)
    {
        printf("The List is Empty\n");
        return;
    }
    //If the data is present in the first node
    if(head->data==n)
    {
        temp=head;
        head=head->next;
        free(temp);
        return;
    }
    nnode=head;

    while(nnode->next->next!=NULL)
    {
        if(nnode->next->data==n)
        {
            temp=nnode->next;
            nnode->next=temp->next;
            free(temp);
            printf("node with value %d is deleted\n",n);
            return;
        }
        else
        {
            nnode=nnode->next;
        }
    }
    //Deleting the last node
    if(nnode->next->data==n)
    {
        temp=nnode->next;
        nnode->next=NULL;
        free(temp);
        printf("The node with value %d is deleted\n",n);
        return;
    }
    //Reached end of list and the item is not present
    printf("The node with value %d is not found\n",n);
    return;
}

void search(int n)
{
    node *nnode;
    nnode=head;
    while(nnode)
    {
        if(nnode->data==n)
        {
            printf("Node with data %d found\n",n);
            return;
        }
        nnode=nnode->next;
    }
    printf("Node with data %d is not found\n",n);
}

void display()
{
    node *nnode;
    if(head==NULL)
    {
        printf("Empty list\n");
        return;
    }
    nnode=head;
    while(nnode)
    {
        printf("%d->",nnode->data);
        nnode=nnode->next;
    }
}

Exercise Programs in Linked list

1. Modify sample program 1 to store items in the reverse order. ie while printing the list the output should be 10 9 8 7 6 5 4 3 2 1.