Skip to main content

Prefix to Postfix Conversion

With a given Prefix Expression, we will see how to convert Prefix Expression into Postfix Expression using stack.
 

Algorithm to convert Prefix Expression to Postfix Expression:

In this algorithm, we will use stack to store operands during the conversion. The step are as follows:
  • Read the prefix string
  • While the end of prefix string scanned from right to left
    • symb = the current character
    • If symb is an operator
      • poped_sym1 = pop the stack
      • poped_sym2 = pop the stack
      • concat the string  STR = (poped_sym1)+(poped_sym2)+ (operator)
      • push the string STR into stack
    • Else
      • push the operand symb into stack
    • End If
  • End While
  • postfix_str = pop the stack


 

Function to convert Prefix Expression to Postfix Expression:


void prefix_to_postfix(char prefix[], char postfix[]){
 char op[2]; //operator string
 char poped1[MAX];
 char poped2[MAX];
 char temp[MAX];
 int i = strlen(prefix);
 op[1] = '\0';
 while(--i != -1){
  if(prefix[i] == ' '){
   continue;
  }
  if(isoperator(prefix[i])){
   pop(poped1);
   pop(poped2);
   op[0] = prefix[i]; //operator
   strcpy(temp, poped1);
   strcat(temp, poped2);
   strcat(temp, op);
   push(temp);
  }
  else{
   op[0] = prefix[i]; //operand
   push(op);
  }
 }
 pop(postfix);
}
 

Program to convert Prefix Expression to Postfix Expression:


#include <stdio.h>
#include <string.h>
#define MAX 30

char stack[MAX][MAX];
int top = -1;

void push(char str[]){
 if(top != MAX-1){
  strcpy(stack[++top], str);
 }
 else{
  printf("Stack overflow : May be invalid postfix expression\n");
 }
}

void pop(char str[]){
 if(top != -1){
  strcpy(str,stack[top--]);
 }
 else{
  printf("Stack underflow : May be invalid postfix expression\n");
 }
}

int isoperator(char c){
 if(c == '+' || c == '-' || c == '*' || c == '/' || c == '^')
  return 1;
 return 0;
}

void prefix_to_postfix(char prefix[], char postfix[]){
 char op[2]; //operator string
 char poped1[MAX];
 char poped2[MAX];
 char temp[MAX];
 int i = strlen(prefix);
 op[1] = '\0';
 while(--i != -1){
  if(prefix[i] == ' '){
   continue;
  }
  if(isoperator(prefix[i])){
   pop(poped1);
   pop(poped2);
   op[0] = prefix[i]; //operator
   strcpy(temp, poped1);
   strcat(temp, poped2);
   strcat(temp, op);
   push(temp);
  }
  else{
   op[0] = prefix[i]; //operand
   push(op);
  }
 }
 pop(postfix);
}

int main(){
 char prefix[] = "+-*^ABCD//EF+GH"; //POSTFIX : AB^C*D-EF/GH+/+
 char postfix[MAX];
 prefix_to_postfix(prefix,postfix);
 printf("Input  Prefix  Expression : %s\n",prefix);
 printf("Output Postfix Expression : %s\n",postfix);
 
 return 0;
}
 
Input  Prefix  Expression : +-*^ABCD//EF+GH
Output Postfix Expression : AB^C*D-EF/GH+/+
 

Related topics:

Labels:

Comments

Post a Comment

Popular posts from this blog

Prefix to Infix Conversion

With a given Prefix Expression, we will see how to convert Prefix Expression into Infix Expression using stack.   Algorithm to convert Prefix Expression to Infix Expression: In this algorithm, we will use stack to store operands during the conversion. The step are as follows: Read the prefix string While the end of prefix string scanned from right to left symb = the current character If symb is an operator poped_sym1 = pop the stack poped_sym2 = pop the stack concat the string  STR = ( poped_sym1 )+ ( operator )+( poped_sym2 ) push the string STR into stack Else push the operand symb into stack End If End While infix_str = pop the stack   Function to convert Prefix Expression to Infix Expression: void prefix_to_infix(char prefix[], char infix[]){ char op[2]; //operator string char poped1[MAX]; char poped2[MAX]; char temp[MAX]; int i = strlen(prefix); op[1] = '\0'; while(--i != -1){ if(prefix[i] == ' '){ continue; } if(isoper...
Post a Comment
Read more

Concatenating two link list

Here we will see how to concat two single link list into other link list. First we copy the content of first list in third list and then the content of second list into third list. Algorithm for concatenation of two link list: This algorithm will use three list. List 1 and List 2 will be concatenated into List 3. The step below: Copy the list 1 into list 3 Copy the list 2 at the last of list 3 Function to concat two link list: void concatLists(NODE **start1, NODE **start2, NODE **mergeinto){ NODE *temp; temp = *start1; while(temp != NULL){ insertAtLast(&*mergeinto, temp->info); temp = temp->next; } temp = *start2; while(temp != NULL){ insertAtLast(&*mergeinto, temp->info); temp = temp->next; } }   Program to concat two link lists: #include <stdio.h> #include <malloc.h> struct node{ int info; struct node *next; }; typedef struct node NODE; void insertAtLast(NODE **, int); void traverse(NODE **); void concatLists(NODE **,...
Post a Comment
Read more

Implementation of Stack to store different data types

Here we will see how to implement stack using structure and union to store different datatypes in stack. First we define the basic structure for elements/items to be stored in the stack. struct Items{ int ele_type; union { int ivalue; float fvalue; char *strvalue; } stack_element; }; In the above code, we have defined a Items structure to store the info about the type of items in ele_type variable and a union variable named stack_element to store the actual value of stack items. In union the, ivalue is used to store the integer value, fvalue to store floating value and strvalue to store the string value. If you wish to add other datatype, you can add any datatype within the union. Now we will define the structure to implement the stack. The code below: struct Stack{ int top; struct Items element[MAX]; }; In the above code, struct Stack is defined to hold the top of stack and the array of Items structure named element to hold the actual Items defined above. MA...
Post a Comment
Read more