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cl1p.net/postfix

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#include<ctype.h>
#include<stdlib.h>
#include <stdio.h>
typedef struct stack
{
    int stck[100];
    int top;
}stack;
int pop(stack *s)
{
    
        return s->stck[(s->top)--];
}
int isempty(stack *s)
{
    if(s->top==-1)
        return 0;
    else
        return 1;
}
void push(stack *s,int value)
{
    s->top++;
    s->stck[s->top]=value;
}
int evaluate(char exp[])
{
    stack s1;
    s1.top=-1;
    int i=0,a,b,res;
    while(exp[i]!='\0')
    {
        if(isdigit(exp[i]))
        {
            
            push(&s1,exp[i]-'0');
        }
        else
        {
            switch(exp[i])
            {
                case '+':
                    a=pop(&s1);
                    b=pop(&s1);
                    res=(b)+(a);
                    break;
                case '-':
                    a=pop(&s1);
                    b=pop(&s1);
                    res=b-a;
                    
                    break;
                case '/':
                    a=pop(&s1);
                    b=pop(&s1);
                    res=b/a;
                    
                    break;
                case '*':
                    a=pop(&s1);
                    b=pop(&s1);
                    res=b*a;
                    
                    break;
            }
            push(&s1,res);
        }
        i=i+1;
    }
return pop(&s1);
}
int main() 
{
    char exp[100];
    printf("Enter the post fix exp\n");
    scanf("%s",exp);
    int res=evaluate(exp);
    printf("res=%d\n",res);
    return 0;
}