Write a C Program to Evaluate Postfix Expression using Stack

1:  #include<stdio.h>  
2:  #include<conio.h>  
3:  #include<string.h>  
4:  #define MAX 50  
5:  int stack[MAX];  
6:  char post[MAX];  
7:  int top=-1;  
8:  void pushstack(int tmp);  
9:  void calculator(char c);  
10:  void main()  
11:  {  
12:   int i;  
13:   clrscr();  
14:   printf("Insert a postfix notation :: ");  
15:   gets(post);  
16:   for(i=0;i<strlen(post);i++)  
17:   {  
18:   if(post[i]>='0' && post[i]<='9')  
19:   {  
20:    pushstack(i);  
21:   }  
22:   if(post[i]=='+' || post[i]=='-' || post[i]=='*' || post[i]=='/' || post[i]=='^')  
23:   {  
24:    calculator(post[i]);  
25:   }  
26:   }  
27:   printf("\n\nResult :: %d",stack[top]);  
28:   getch();  
29:  }  
30:  void pushstack(int tmp)  
31:  {  
32:   top++;  
33:   stack[top]=(int)(post[tmp]-48);  
34:  }  
35:  void calculator(char c)  
36:  {  
37:   int a,b,ans;  
38:   a=stack[top];  
39:   stack[top]='\0';  
40:   top--;  
41:   b=stack[top];  
42:   stack[top]='\0';  
43:   top--;  
44:   switch(c)  
45:   {  
46:   case '+':  
47:   ans=b+a;  
48:   break;  
49:   case '-':  
50:   ans=b-a;  
51:   break;  
52:   case '*':  
53:   ans=b*a;  
54:   break;  
55:   case '/':  
56:   ans=b/a;  
57:   break;  
58:   case '^':  
59:   ans=b^a;  
60:   break;  
61:   default:  
62:   ans=0;  
63:   }  
64:   top++;  
65:   stack[top]=ans;  
66:  }