Slip 24 - A) Write a ‘C’ program to read a postfix expression, evaluate it and display the result. (Use Dynamic Implementation of Stack)

Solution:

#include<stdio.h>

#include<conio.h>

#include<math.h>

char st[100];

int top=-1;

void push(char c)

{

top++;

st[top]=c;

}

char pop()

{

char c;

c=st[top];

top–;

return c;

}

int main()

{

int i,j,p,a,b,temp;

char s1[30];

clrscr();

printf(“\nEnter the Postfix Expr”);

gets(s1);

j=0;

for(i=0;s1[i]!=”;i++)

{

if(s1[i]<=’9′ && s1[i]>=’0′)

push(s1[i]-48);

else

{

a=pop();

b=pop();

switch(s1[i])

{

case ‘+’:

temp=b+a;

break;

case ‘-‘:

temp=b-a;

break;

case ‘/’: temp=b/a;

break;

case ‘*’:

temp=b*a;

break;

case ‘^’:

temp=pow(b,a);

break;

case ‘%’:

temp=b%a;

break;

}

push(temp);

}

}

j=pop();

printf(“Result is %d “,j);

getch();

return;

}