Postfix Evaluation

PROGRAM:

#include<stdio.h>
#include<string.h>
#include<conio.h>
void push(int);
int pop();
int stack[20],top=-1;
void main()
{
 char expr[20];
 int len,a,b,c,i,x;
 clrscr();
 printf("$$$ POSTFIX EVALUATION $$$");
 printf("\nEnter the postfix expression:");
 scanf("%s",expr);
 len=strlen(expr);
 for(i=0;i<len;i++)
 {
  if(expr[i]=='+'||expr[i]=='-'||expr[i]=='*'||expr[i]=='/')
  {
   b=pop();
   a=pop();
   switch(expr[i])
   {
    case '+':c=a+b;
      push(c);
      break;
    case '-':c=a-b;
      push(c);
      break;
    case '*':c=a*b;
      push(c);
      break;
    case '/':c=a/b;
      push(c);
      break;
   }
  }
  else
  {
   printf("Enter the value of %c:",expr[i]);
   scanf("%d",&x);
   push(x);
  }
 }
 printf("The resultant value is : %d",stack[top]);
 getch();
}
void push(int item)
{
 stack[++top]=item;
}
int pop()
{
 int a;
 a=stack[top];
 top=top-1;
 return a;
}


OUTPUT:

$$$ POSTFIX EVALUATION $$$

Enter the postfix expression: abc+*
Enter the value of a: 10
Enter the value of b: 20
Enter the value of c: 30
The resultant value is : 500

Balancing Symbol

PROGRAM:

#include<stdio.h>

#include<conio.h>

void main()

{

                int top=-1,d=0;

                char ch,stack[30];

                clrscr();

                printf("\n\n$$$ BALANCING SYMBOLS $$$\n\n");

                printf("Check whether the given expression is balanced or not\n");

                printf("Enter the expression:\t");

                while(ch=getchar(),ch!='#')

                {

                                switch(ch)

                                {

                                                case '(':stack[++top]=ch;break;

                                                case '{':stack[++top]=ch;break;

                                                case '[':stack[++top]=ch;break;

                                                case ')':if(stack[top]=='(')

                                                                 {

                                                                                top=top-1;

                                                                 }

                                                                 else

                                                                 {

                                                                                d=d+1;

                                                                 }

                                                                 break;

                                                case '}':if(stack[top]=='{')

                                                                 {

                                                                                top=top-1;

                                                                 }

                                                                 else

                                                                 {

                                                                                d=d+1;

                                                                 }

                                                                 break;

                                                case ']':if(stack[top]=='[')

                                                                 {

                                                                                top=top-1;

                                                                 }

                                                                 else

                                                                 {

                                                                                d=d+1;

                                                                 }

                                                                 break;

                                }

                }

                if(top==-1 && d==0)

                {

                                printf("Balanced Expression\n");

                }

                else

                {

                                printf("Unbalanced Expression\n");

                }

                getch();

}

OUTPUT:

$$$ BALANCING SYMBOLS $$$

Check whether the given expression is balanced or not

Enter the expression:   {[(a+b)*c]-[(c*d)+b]}#

Balanced Expression

$$$ BALANCING SYMBOLS $$$

Check whether the given expression is balanced or not

Enter the expression:   {(a*b]/(c+d]}#

Unbalanced Expression

Infix to Postfix Conversion

PROGRAM:

#include<stdio.h>

#include<conio.h>

#define SIZE 50

void push(char);

char pop();

int priority(char);

char s[SIZE];

int top=-1;

void main()

{

                char infix[50],postfix[50],ch,item;

                int i=0,k=0,len;

                clrscr();

                printf("\n\n $$$ INFIX TO POSTFIX CONVERSION $$$ \n\n");

                printf("Enter infix expression:\t");

                scanf("%s",infix);

                push('#');

                len=strlen(infix);

                for(i=0;i<len;i++)

                {

                                ch=infix[i];

                                if(isalnum(ch))

                                {

                                                postfix[k]=ch;

                                                k++;

                                }

                                else if(ch=='(')

                                {

                                                push(ch);

                                }

                                else if(ch==')')

                                {

                                                while(s[top]!='(')

                                                {

                                                                postfix[k]=pop();

                                                                k++;

                                                }

                                                item=pop();

                                }

                                else

                                {

                                                while(priority(s[top])>=priority(ch))

                                                {

                                                                postfix[k]=pop();

                                                                k++;

                                                }

                                                push(ch);

                                }

                }

                while(s[top]!='#')

                {

                                postfix[k]=pop();

                                k++;

                }

                postfix[k]='\0';

                printf("Postfix expression is: %s",postfix);

                getch();

}

void push(char a)

{

                top=top+1;

                s[top]=a;

}

char pop()

{

                char a;

                a=s[top];

                top=top-1;

                return a;

}

int priority(char a)

{

                switch(a)

                {

                                case '#':return 0;

                                case '(':return 1;

                                case '+':return 2;

                                case '-':return 2;

                                case '*':return 3;

                                case '/':return 3;

                                case '^':return 4;

                }

}

OUTPUT:

$$$ INFIX TO POSTFIX CONVERSION $$$

Enter infix expression: (A+B^C)*D+E^5

Postfix expression is: ABC^+D*E5^+