C - Program for Expression Conversion
/* C - Program for conversion of :
1. infix to its postfix form
2. infix to its prefix form
3. Evaluation of postfix expression
operators supported '+,-,*,/,%,^,(,)
operands supported -- all single character operands
*/
#include<stdio.h>
#include<conio.h>
#include<ctype.h>
#define MAX 50
typedef struct node
{
int data;
struct node *next;
}node;
int precedence(char);
void init(node **);
int empty(node *);
int pop(node **);
void push(node **,int );
int top(node *); //value of the top element
void infix_to_prefix(char infix[],char prefix[]);
void infix_to_postfix(char infix[],char postfix[]);
void eval_postfix(char postfix[]);
int evaluate(char x,int op1,int op2);
void main()
{
char infix[30],postfix[30],prefix[30];
clrscr();
printf("\nEnter an infix expression : ");
gets(infix);
infix_to_postfix(infix,postfix);
infix_to_prefix(infix,prefix);
printf("\nPostfix : %s\nprefix: %s ",postfix,prefix);
printf("\nPostfix evaluation : ");
eval_postfix(postfix);
getch();
}
void infix_to_prefix(char infix[],char prefix[])
{
int i,j;
char temp,in1[30];
// reverse the infix expression and store it in in1[]
for(i=strlen(infix)-1,j=0;i>=0;i--,j++)
in1[j]=infix[i];
in1[j]='\0';
// reverse the direction of brackets
for(i=0;in1[i]!='\0';i++)
{
if(in1[i]=='(')
in1[i]=')';
else
if(in1[i]==')')
in1[i]='(';
}
// convert from infix to postfix
infix_to_postfix(in1,prefix);
//reverse the final expression
for(i=0,j=strlen(prefix)-1;i<j;i++,j--)
{
temp=prefix[i];
prefix[i]=prefix[j];
prefix[j]=temp;
}
}
void infix_to_postfix(char infix[],char postfix[])
{
node *head;
char x;
int i,j;//i-index for infix[],j-index for postfix
char token;
init(&head);
j=0;
for(i=0;infix[i]!='\0';i++)
{
token=infix[i];
if(isalnum(token))
postfix[j++]=token;
else
if(token == '(')
push(&head,'(');
else
if(token == ')')
while((x=pop(&head))!='(')
postfix[j++]=x;
else
{
while(precedence(token)<=precedence(top(head)) && !empty(head))
{
x=pop(&head);
postfix[j++]=x;
}
push(&head,token);
}
}
while(!empty(head))
{
x=pop(&head);
postfix[j++]=x;
}
postfix[j]='\0';
}
void eval_postfix(char postfix[])
{
node *head;
char x;
int op1,op2,val,i;
init(&head);
for(i=0;postfix[i]!='\0';i++)
{ x=postfix[i];
if(isalpha(x))
{ printf("\nEnter the value of %c : ",x);
scanf("%d",&val);
push(&head,val);
}
else
{ //pop two operands and evaluate
op2=pop(&head);
op1=pop(&head);
val=evaluate(x,op1,op2);
push(&head,val);
}
}
val=pop(&head);
printf("\nvalue of expression = %d",val);
}
int evaluate(char x,int op1,int op2)
{
if(x=='+') return(op1+op2);
if(x=='-') return(op1-op2);
if(x=='*') return(op1*op2);
if(x=='/') return(op1/op2);
if(x=='%') return(op1%op2);
}
int precedence(char x)
{
if(x == '(') return(0);
if(x == '+' || x == '-') return(1);
if(x == '*' || x == '/' || x == '%') return(2);
return(3);
}
void init(node **head)
{
*head=NULL;
}
int empty(node *head)
{
if(head==NULL)
return(1);
return(0);
}
void push(node **head,int x)
{
node *p;
p=(node*)malloc(sizeof(node));
p->data=x;
p->next=*head;
*head=p;
}
int pop(node **head)
{
int x;
node *p;
p=*head;
*head=p->next;
x=p->data;
free(p);
return(x);
}
int top(node *head)
{
return(head->data);
}
#include<stdio.h>
#include<conio.h>
#include<ctype.h>
#define MAX 50
typedef struct node
{
int data;
struct node *next;
}node;
int precedence(char);
void init(node **);
int empty(node *);
int pop(node **);
void push(node **,int );
int top(node *); //value of the top element
void infix_to_prefix(char infix[],char prefix[]);
void infix_to_postfix(char infix[],char postfix[]);
void eval_postfix(char postfix[]);
int evaluate(char x,int op1,int op2);
void main()
{
char infix[30],postfix[30],prefix[30];
clrscr();
printf("\nEnter an infix expression : ");
gets(infix);
infix_to_postfix(infix,postfix);
infix_to_prefix(infix,prefix);
printf("\nPostfix : %s\nprefix: %s ",postfix,prefix);
printf("\nPostfix evaluation : ");
eval_postfix(postfix);
getch();
}
void infix_to_prefix(char infix[],char prefix[])
{
int i,j;
char temp,in1[30];
// reverse the infix expression and store it in in1[]
for(i=strlen(infix)-1,j=0;i>=0;i--,j++)
in1[j]=infix[i];
in1[j]='\0';
// reverse the direction of brackets
for(i=0;in1[i]!='\0';i++)
{
if(in1[i]=='(')
in1[i]=')';
else
if(in1[i]==')')
in1[i]='(';
}
// convert from infix to postfix
infix_to_postfix(in1,prefix);
//reverse the final expression
for(i=0,j=strlen(prefix)-1;i<j;i++,j--)
{
temp=prefix[i];
prefix[i]=prefix[j];
prefix[j]=temp;
}
}
void infix_to_postfix(char infix[],char postfix[])
{
node *head;
char x;
int i,j;//i-index for infix[],j-index for postfix
char token;
init(&head);
j=0;
for(i=0;infix[i]!='\0';i++)
{
token=infix[i];
if(isalnum(token))
postfix[j++]=token;
else
if(token == '(')
push(&head,'(');
else
if(token == ')')
while((x=pop(&head))!='(')
postfix[j++]=x;
else
{
while(precedence(token)<=precedence(top(head)) && !empty(head))
{
x=pop(&head);
postfix[j++]=x;
}
push(&head,token);
}
}
while(!empty(head))
{
x=pop(&head);
postfix[j++]=x;
}
postfix[j]='\0';
}
void eval_postfix(char postfix[])
{
node *head;
char x;
int op1,op2,val,i;
init(&head);
for(i=0;postfix[i]!='\0';i++)
{ x=postfix[i];
if(isalpha(x))
{ printf("\nEnter the value of %c : ",x);
scanf("%d",&val);
push(&head,val);
}
else
{ //pop two operands and evaluate
op2=pop(&head);
op1=pop(&head);
val=evaluate(x,op1,op2);
push(&head,val);
}
}
val=pop(&head);
printf("\nvalue of expression = %d",val);
}
int evaluate(char x,int op1,int op2)
{
if(x=='+') return(op1+op2);
if(x=='-') return(op1-op2);
if(x=='*') return(op1*op2);
if(x=='/') return(op1/op2);
if(x=='%') return(op1%op2);
}
int precedence(char x)
{
if(x == '(') return(0);
if(x == '+' || x == '-') return(1);
if(x == '*' || x == '/' || x == '%') return(2);
return(3);
}
void init(node **head)
{
*head=NULL;
}
int empty(node *head)
{
if(head==NULL)
return(1);
return(0);
}
void push(node **head,int x)
{
node *p;
p=(node*)malloc(sizeof(node));
p->data=x;
p->next=*head;
*head=p;
}
int pop(node **head)
{
int x;
node *p;
p=*head;
*head=p->next;
x=p->data;
free(p);
return(x);
}
int top(node *head)
{
return(head->data);
}