| #include<stdio.h> #include<string.h> #include<stdlib.h> struct node { char c; struct node *left; struct node *right; }; struct node *stk[20], *temp, *root; char postfix[20],ch; int top=-1, max=20, len; void preorder(struct node*); void exptree(); void push(struct node*); struct node* pop(); int main() { printf(“Enter Postfix expression : “); scanf(“%s”, postfix); exptree(); printf(“Prefix expression is : “); preorder(root); return 0; } void preorder(struct node *p) { if(p != NULL) { printf(“%c”, p->c); preorder(p->left); preorder(p->right); } } void exptree() { int i, j; i=0; j = strlen(postfix); while(i<j) { switch(postfix[i]) { case ‘+’ : case ‘-‘ : case ‘*’ : case ‘/’ : case ‘%’ : temp = (struct node*)malloc(sizeof(struct node)); temp->c = postfix[i]; temp->right = pop(); temp->left = pop(); push(temp); break; default : temp = (struct node*)malloc(sizeof(struct node)); temp->c = postfix[i]; temp->left = NULL; temp->right = NULL; push(temp); break; } ++i; } root = pop(); } void push(struct node *p) { if(top==max) printf(“Stack is Full \n”); else stk[++top] = p; } struct node* pop() { if(top==-1) printf(“Invalid expression \n”); else return stk[top–]; } |