#include <stdio.h>
#include <conio.h>
#include <ctype.h>
#include <string.h>
#define MAX 100
char st[MAX];
int top=–1;
void push(char st[], char);
char pop(char st[]);
void InfixtoPostfix(char source[], char target[]);
int getPriority(char);
int main()
{
char infix[100], postfix[100];
clrscr();
printf("\n Enter any infix expression : ");
gets(infix);
strcpy(postfix, "");
InfixtoPostfix(infix, postfix);
printf("\n The corresponding postfix expression is : ");
puts(postfix);
getch();
return 0;
}
void InfixtoPostfix(char source[], char target[])
{
int i=0, j=0;
char temp;
strcpy(target, "");
while(source[i]!='\0')
{
if(source[i]=='(')
{
push(st, source[i]);
i++;
}
else if(source[i] == ')')
{
while((top!=–1) && (st[top]!='('))
{
target[j] = pop(st);
j++;
}
if(top==–1)
{
printf("\n INCORRECT EXPRESSION");
exit(1);
}
temp = pop(st);
//remove left parenthesis
i++;
}
else if(isdigit(source[i]) || isalpha(source[i]))
 {
 target[j] = source[i];
j++;
i++;
}
else if (source[i] == '+' || source[i] == '–' || source[i] == '*' || source[i] == '/' || source[i] == '%')
{
while( (top!=–1) && (st[top]!= '(') && (getPriority(st[top])
> getPriority(source[i])))
{
target[j] = pop(st);
j++;
}
push(st, source[i]);
i++;
}
else
{
printf("\n INCORRECT ELEMENT IN EXPRESSION");
exit(1);
}
}
//end of while loop
while((top!=–1) && (st[top]!='('))
{
target[j] = pop(st);
j++;
}
target[j]='\0';
}
// method end

int getPriority(char op)
{
if(op=='/' || op == '*' || op=='%')
return 1;
else if(op=='+' || op=='–')
return 0;
}
void push(char st[], char val)
{
if(top==MAX–1)
printf("\n STACK OVERFLOW");
else
{
top++;
st[top]=val;
}
}
char pop(char st[])
{
char val=' ';
if(top==–1)
printf("\n STACK UNDERFLOW");
else
{
val=st[top];
top––;
}
return val;
}