#include <stdio.h>
#include <ctype.h>
#include <string.h>
#include <limits.h>
#include <stdlib.h>
#define MAX 100 // Maximum size of stack
char stk[100];
int top = -1;
int isEmpty()
{
return top == -1;
}
int isFull()
{
return top == MAX - 1;
}
char peek()
{
return stk[top];
}
char pop()
{
if(isEmpty())
return -1;
char ch = stk[top];
top--;
return(ch);
}
void push(char oper)
{
if(isFull())
printf("Stack Full!!!!"); else{
top++;
stk[top] = oper;
}
}
int checkIfOperand(char ch)
{
return (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z');
}
int precedence(char ch)
{
switch (ch)
{
case '+':
case '-':
return 1;
case '*':
case '/':
return 2;
case '^':
return 3;
}
return -1;
}
int covertInfixToPostfix(char* expression)
{
int i, j;
for (i = 0, j = -1; expression[i]; ++i)
{
if (checkIfOperand(expression[i]))
expression[++j] = expression[i];
else if (expression[i] == '(')
push(expression[i]);
else if (expression[i] == ')')
{
while (!isEmpty() && peek() != '(')
expression[++j] = pop();
if (!isEmpty() && peek() != '(')
return -1;
else
pop();
}
else
{
while (!isEmpty() && precedence(expression[i]) <= precedence(peek()))
expression[++j] = pop();
push(expression[i]);
}
}
while (!isEmpty())
expression[++j] = pop();
expression[++j] = '\0';
printf( "%s", expression);
}
int main()
{
char expression[MAX];
printf("Enter an infix expression: ");
fgets(expression, MAX, stdin);
covertInfixToPostfix(expression);
return 0;
}
