Program for evaluation of postfix expression .

 Here we get input of  postfix expression in string for and check character one by one if character is an operator then perform operation otherwise  first change in to ascii number and create a number  by number*10+(ascii-48)  while ascii is in range[48(for 0) to 57(for 9)]  . 

#include<stdio.h>

#include<string.h>

#include<math.h>

# define max 50

int stack[max] ;

int top=-1;

void push(int element)

{

top=top+1;

stack[top]=element;

}

int pop()

{

int element;

if(top==-1)

printf("Stack is underflow");

else

{

element=stack[top];

top-=1;

return element;

}

}

int main()

{

char postfix[50];

int length,a,b,c,i,num,ascii;

printf("Enter postfix expression value seprated by comma");

gets(postfix);

length=strlen(postfix);

postfix[length]=')';

for(i=0;postfix[i]!=')';i++)

{

if(postfix[i]==' ')

continue;

if(postfix[i]=='+'||postfix[i]=='-'||postfix[i]=='*'||postfix[i]=='/'||postfix[i]=='^')

{

a=pop();

b=pop();

if(postfix[i]=='+')

c=b+a;

if(postfix[i]=='-')

c=b-a;

if(postfix[i]=='*')

c=b*a;

if(postfix[i]=='/')

c=b/a;

if(postfix[i]=='^')

c=pow(b,a);

push(c);

}

else

{

num=0;

ascii=postfix[i];

while(ascii>=48&&ascii<=57)

{

num=num*10+(ascii-48);

i+=1;

ascii=postfix[i];

}

push(num);

}

}

printf("result = %d ",stack[top]);

return 0;

}