C Program to Convert Infix to Postfix Expression using Stack

GTU Data Structure Practical - 4

Implement a program to convert Infix to Postfix notation using Stack.

				
					#include<stdio.h>
#include<stdlib.h>  
#include<ctype.h>
#include<string.h>

#define SIZE 100

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

void push(char item)
{
  if(top >= SIZE-1)
  {
    printf("\nStack Overflow.");
  }
  else
  {
    top = top+1;
    stack[top] = item;
  }
}

char pop()
{
  char item ;

  if(top <0)
  {
    printf("stack under flow: invalid infix expression");
    getchar();
    /* underflow may occur for invalid expression */
    /* where ( and ) are not matched */
    exit(1);
  }
  else
  {
    item = stack[top];
    top = top-1;
    return(item);
  }
}

int is_operator(char symbol)
{
  if(symbol == '^' || symbol == '*' || symbol == '/' || symbol == '+' || symbol =='-')
  {
    return 1;
  }
  else
  {
  return 0;
  }
}

int precedence(char symbol)
{
  if(symbol == '^')
  {
    return(3);
  }
  else if(symbol == '*' || symbol == '/')
  {
    return(2);
  }
  else if(symbol == '+' || symbol == '-')          
  {
    return(1);
  }
  else
  {
    return(0);
  }
}

void InfixToPostfix(char infix_exp[], char postfix_exp[])
{ 
  int i, j;
  char item;
  char x;

  push('(');                               
  strcat(infix_exp,")");                

  i=0;
  j=0;
  item=infix_exp[i];        

  while(item != '<pre data-line="" class="highlight-height language-c line-numbers">
				<code readonly="true" class="language-c">
					<xmp>#include<stdio.h>
#include<stdlib.h>  
#include<ctype.h>
#include<string.h>

#define SIZE 100

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

void push(char item)
{
  if(top >= SIZE-1)
  {
    printf("\nStack Overflow.");
  }
  else
  {
    top = top+1;
    stack[top] = item;
  }
}

char pop()
{
  char item ;

  if(top <0)
  {
    printf("stack under flow: invalid infix expression");
    getchar();
    /* underflow may occur for invalid expression */
    /* where ( and ) are not matched */
    exit(1);
  }
  else
  {
    item = stack[top];
    top = top-1;
    return(item);
  }
}

int is_operator(char symbol)
{
  if(symbol == '^' || symbol == '*' || symbol == '/' || symbol == '+' || symbol =='-')
  {
    return 1;
  }
  else
  {
  return 0;
  }
}

int precedence(char symbol)
{
  if(symbol == '^')
  {
    return(3);
  }
  else if(symbol == '*' || symbol == '/')
  {
    return(2);
  }
  else if(symbol == '+' || symbol == '-')          
  {
    return(1);
  }
  else
  {
    return(0);
  }
}

void InfixToPostfix(char infix_exp[], char postfix_exp[])
{ 
  int i, j;
  char item;
  char x;

  push('(');                               
  strcat(infix_exp,")");                

  i=0;
  j=0;
  item=infix_exp[i];        

  while(item != '\0') 
  {
    if(item == '(')
    {
      push(item);
    }
    else if( isdigit(item) || isalpha(item))
    {
      postfix_exp[j] = item;              
      j++;
    }
    else if(is_operator(item) == 1)        
    {
      x=pop();
      while(is_operator(x) == 1 && precedence(x)>= precedence(item))
      {
        postfix_exp[j] = x;                  
        j++;
        x = pop();                       
      }
      push(x);

      push(item);                
    }
    else if(item == ')')        
    {
      x = pop();                  
      while(x != '(')                
      {
        postfix_exp[j] = x;
        j++;
        x = pop();
      }
    }
    else
    {
      printf("\nInvalid infix Expression.\n");       
      getchar();
      exit(1);
    }
    i++;


    item = infix_exp[i]; 
  } 
  if(top>0)
  {
    printf("\nInvalid infix Expression.\n");        
    getchar();
    exit(1);
  }
  if(top>0)
  {
    printf("\nInvalid infix Expression.\n");        
    getchar();
    exit(1);
  }

  postfix_exp[j] = '\0';
  
}

int main()
{
  char infix[SIZE], postfix[SIZE];         

  printf("ASSUMPTION: The infix expression contains single letter variables and single digit constants only.\n");
  printf("\nEnter Infix expression : ");
  gets(infix);

  InfixToPostfix(infix,postfix);                   
  printf("Postfix Expression: ");
  puts(postfix);                     

  return 0;
}

') { if(item == '(') { push(item); } else if( isdigit(item) || isalpha(item)) { postfix_exp[j] = item; j++; } else if(is_operator(item) == 1) { x=pop(); while(is_operator(x) == 1 && precedence(x)>= precedence(item)) { postfix_exp[j] = x; j++; x = pop(); } push(x); push(item); } else if(item == ')') { x = pop(); while(x != '(') { postfix_exp[j] = x; j++; x = pop(); } } else { printf("\nInvalid infix Expression.\n"); getchar(); exit(1); } i++; item = infix_exp[i]; } if(top>0) { printf("\nInvalid infix Expression.\n"); getchar(); exit(1); } if(top>0) { printf("\nInvalid infix Expression.\n"); getchar(); exit(1); } postfix_exp[j] = '

				
					#include<stdio.h>
#include<stdlib.h>  
#include<ctype.h>
#include<string.h>

#define SIZE 100

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

void push(char item)
{
  if(top >= SIZE-1)
  {
    printf("\nStack Overflow.");
  }
  else
  {
    top = top+1;
    stack[top] = item;
  }
}

char pop()
{
  char item ;

  if(top <0)
  {
    printf("stack under flow: invalid infix expression");
    getchar();
    /* underflow may occur for invalid expression */
    /* where ( and ) are not matched */
    exit(1);
  }
  else
  {
    item = stack[top];
    top = top-1;
    return(item);
  }
}

int is_operator(char symbol)
{
  if(symbol == '^' || symbol == '*' || symbol == '/' || symbol == '+' || symbol =='-')
  {
    return 1;
  }
  else
  {
  return 0;
  }
}

int precedence(char symbol)
{
  if(symbol == '^')
  {
    return(3);
  }
  else if(symbol == '*' || symbol == '/')
  {
    return(2);
  }
  else if(symbol == '+' || symbol == '-')          
  {
    return(1);
  }
  else
  {
    return(0);
  }
}

void InfixToPostfix(char infix_exp[], char postfix_exp[])
{ 
  int i, j;
  char item;
  char x;

  push('(');                               
  strcat(infix_exp,")");                

  i=0;
  j=0;
  item=infix_exp[i];        

  while(item != '\0') 
  {
    if(item == '(')
    {
      push(item);
    }
    else if( isdigit(item) || isalpha(item))
    {
      postfix_exp[j] = item;              
      j++;
    }
    else if(is_operator(item) == 1)        
    {
      x=pop();
      while(is_operator(x) == 1 && precedence(x)>= precedence(item))
      {
        postfix_exp[j] = x;                  
        j++;
        x = pop();                       
      }
      push(x);

      push(item);                
    }
    else if(item == ')')        
    {
      x = pop();                  
      while(x != '(')                
      {
        postfix_exp[j] = x;
        j++;
        x = pop();
      }
    }
    else
    {
      printf("\nInvalid infix Expression.\n");       
      getchar();
      exit(1);
    }
    i++;


    item = infix_exp[i]; 
  } 
  if(top>0)
  {
    printf("\nInvalid infix Expression.\n");        
    getchar();
    exit(1);
  }
  if(top>0)
  {
    printf("\nInvalid infix Expression.\n");        
    getchar();
    exit(1);
  }

  postfix_exp[j] = '\0';
  
}

int main()
{
  char infix[SIZE], postfix[SIZE];         

  printf("ASSUMPTION: The infix expression contains single letter variables and single digit constants only.\n");
  printf("\nEnter Infix expression : ");
  gets(infix);

  InfixToPostfix(infix,postfix);                   
  printf("Postfix Expression: ");
  puts(postfix);                     

  return 0;
}

'; } int main() { char infix[SIZE], postfix[SIZE]; printf("ASSUMPTION: The infix expression contains single letter variables and single digit constants only.\n"); printf("\nEnter Infix expression : "); gets(infix); InfixToPostfix(infix,postfix); printf("Postfix Expression: "); puts(postfix); return 0; }

C Program to Convert Infix to Postfix Expression using Stack

GTU Data Structure Practical - 4

Implement a program to convert Infix to Postfix notation using Stack.

Output

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