Stack Program #5

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19. Write a program for evaluation of post-fix expression using Stack.




#include<stdio.h>
#define N 50
char s[N];
int top=-1;
void push(int);
int pop();
int perform(int oprand1,int oprand2,char temp);
void main()
{
     int i=0,value=0,oprand1,oprand2,x,result,j;
     char postfix[50],temp;
     printf("Enter the postfix expression:\n");
     scanf("%s",postfix);
     temp=postfix[i];
     while(temp!='\0')
     {
     if(temp>='0' && temp<='9')
     {
          push(temp-'0');
     }
     else
     {
          oprand2=pop();
          oprand1=pop();
          value=perform(oprand1,oprand2,temp);
          push(value);
          printf ("%c\t", temp);
     }
     printf("\nThe stack is\n");
     for (j=top;j>=0;j--)
     {
          
           printf ("%d\n", s[j]);
     }
     i++;
     temp=postfix[i];
     }
     result=pop();
     printf("Evaluation of postfix exp. is %d\n",result);
}
void push(int x)
{
     if(top>=N-1)
     {
         
          printf("STACK OVERFLOW\n");
     }
     else
     {
          top++;
          s[top]=x;
     }
}
int pop()
{
     if(top==-1)
     {
          printf("STACK UNDERFLOW\n");
          return('\0');
     }
     else
     {
          top=top-1;
          return(s[top+1]);
     }
}
int perform(int oprand1,int oprand2,char temp)
{
     int j=1,ans;
     if(temp=='+')
     {
          return(oprand1+oprand2);
     }
     else if(temp=='-')
     {
          return(oprand1-oprand2);
     }
      else if(temp=='*')
     {
          return(oprand1*oprand2);
     }
      else if(temp=='/')
     {
          return(oprand1/oprand2);
     }
      else if(temp=='^' || temp=='$')
     {
          for(j=1;j<=oprand2;j++)
          {
               ans=oprand1*ans;
          }
          return(ans);
     }
}

OR

#include<stdio.h>
#include<ctype.h>
#include<math.h>
#define N 50
char s[N];
int top=-1;
void push(int);
int pop();
int perform(int oprand1,int oprand2,char temp);
void main()
{
     int i=0,value=0,oprand1,oprand2,x,result;
     char postfix[50],temp;
     printf("Enter the postfix expression:\n");
     scanf("%s",postfix);
     temp=postfix[i];
     while(temp!='\0')
     {
     if(isdigit(temp))
     {
          push(temp-'0');
     }
     else
     {
          oprand2=pop();
          oprand1=pop();
          value=perform(oprand1,oprand2,temp);
          push(value);
     }
     i++;
     temp=postfix[i];
     }
     result=pop();
     printf("Evaluation of postfix exp. is %d\n",result);
}   
void push(int x)
{
     if(top>=N-1)
     {
         
          printf("STACK OVERFLOW\n");
     }
     else
     {
          top++;
          s[top]=x;
     }
}
int pop()
{
     if(top==-1)
     {
          printf("STACK UNDERFLOW\n");
          return('\0');
     }
     else
     {
          top=top-1;
          return(s[top+1]);
     }
}
int perform(int oprand1,int oprand2,char temp)
{
    int j=1,ans;
     if(temp=='+')
     {
          return(oprand1+oprand2);
     }
     else if(temp=='-')
     {
          return(oprand1-oprand2);
     }
      else if(temp=='*')
     {
          return(oprand1*oprand2);
     }
      else if(temp=='/')
     {
          return(oprand1/oprand2);
     }
      else if(temp=='^' || temp=='$')
     {
          for(j=1;j<=oprand2;j++)
          {
               ans=oprand1*ans;
          }
          return(ans);
     }
}

Output

  1.  Enter the postfix expression:
    752+*411+/-

    The stack is
    7

    The stack is
    5
    7

    The stack is
    2
    5
    7
    +  
    The stack is
    7
    7
    *  
    The stack is
    49

    The stack is
    4
    49

    The stack is
    1
    4
    49

    The stack is
    1
    1
    4
    49
    +  
    The stack is
    2
    4
    49
    /  
    The stack is
    2
    49
    -  
    The stack is
    47
    Evaluation of postfix exp. is 47






OR

Output

  1. Enter the postfix expression:
    752+*411+/-
    Evaluation of postfix exp. is 47
     



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