#include<stdio.h>
#include<string.h>
#define size 20
void streverse(char*);
int push(int x);
int pop();
int evalprefix();
int eval(int,int,char);
struct stack
{
int b[size];
int top;
}s;
int main()
{
s.top=-1;
int y;
char ch;
y=evalprefix();
printf("Evalution of prefix expression is %d",y);
return 0;
}
int evalprefix()
{
char a[size];
char *x;
printf("Enter prefix expression:\t");
scanf("%s",a);
streverse(a);
int i=0,op1,op2,r,y;
char ch;
while((ch=a[i])!='\0')
{
if((ch>='0')&&(ch<='9'))
push(ch-'0');
else{
op1=pop();
op2=pop();
r=eval(op1,op2,ch);
push(r);
}
i++;
}
y=pop();
return y;
}
int eval(int a,int b,char c)
{
switch(c)
{
case '+':return(a+b);
case '-':return(a-b);
case '*':return(a*b);
case '/':return(a/b);
}
}
int push(int x)
{
s.top++;
s.b[s.top]=x;
return(s.b[s.top]);
}
int pop()
{
return(s.b[s.top--]);
}
void streverse(char* str) {
int len = strlen(str);
char a[len];
int i;
for ( i = 0; i < len; i++) {
a[i] = str[len - 1 - i];
};
for ( i = 0; i < len; i++) {
str[i] = a[i];
}
}