Evaluate Postfix

#include<stdio.h>
#include<conio.h>
#include<string.h>
int s[100],top=-1;
int operand(char x){
	return ((x>='a'&&x<='z')||(x<='A'&&x<='Z'));
}

void push(int a){
	top++;
	s[top]=a;
}
int pop(){
	return s[top--];
}
int main(){
int i=0,n,a,b,result;
char str[30];
clrscr();
printf("Enter postfix Expression: ");
scanf("%s",str);
//n=strlen(str);
while(s[i]!=')'){
	if(operand(str[i])){
	 int a=pop();
	 int b=pop();
		if(str[i]=='+'){
			result=b+a;
		}else if(str[i]=='-'){
			result=b-a;
		}else if(str[i]=='*'){
			result=b*a;
		}else if(str[i]=='/'){
			result=b/a;
		}else{
			continue;
		}
		push(result);
	}else{
		push(str[i]);
	}
	i++;

}
printf("Result: %d",pop());
getch();
return 0;
}