infix_to_postfix.c File Reference

Infix to Postfix Expression Conversion More...

#include <stdio.h>

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Data Structures
struct	Stack
	for printf() and scanf() More...

Functions
void	push (struct Stack *p, char x)
	push function More...
char	pop (struct Stack *p)
	pop function More...
int	isOprnd (char ch)
	isOprnd function More...
int	isEmpty (struct Stack s)
	isEmpty function More...
int	getPrecedence (char op1, char op2)
	getPrecedence function returns the precedence after comparing two operators passed as parameter. More...
void	convert (char infix[], char postfix[])
	convert function More...
int	main ()
	main function More...

Detailed Description

Infix to Postfix Expression Conversion

Convert Infixed expressions to Postfix expression.

Author

Harsh Karande

Function Documentation

convert()

void convert	(	char	infix[],
		char	postfix[]
	)

convert function

Parameters

infix[]	: infix array provided by user
postfix[]	: empty array to be given to convert()

Returns

postfixed expresion or \0 on exit

{
    struct Stack s;  // initialze object reference of stack
    s.tos = -1;      // initalize the tos
 
    int i, j = 0, pr;
    char ch, temp;
 
    for (i = 0; infix[i] != '\0'; i++)
    {
        ch = infix[i];
 
        if (isOprnd(ch) == 1)  // check if char is operand or operator
        {
            postfix[j] = ch;  // assign ch to postfix array with index j
            j++;              // incement j
        }
        else
        {
            if (ch == '(')
            {
                push(&s, ch);
            }
            else
            {
                if (ch == ')')
                {
                    while ((temp = pop(&s)) != '(')
                    {
                        postfix[j] = temp;
                        j++;
                    }
                }
                else
                {
                    while (isEmpty(s) == 0)  // check if stack is empty
                    {
                        pr = getPrecedence (ch,
                                   s.arr[s.tos]);  // check operator precedence
 
                        if (pr == 1)
                        {
                            break;  // if ch has a greater precedence than
                                    // s.arr[s.top]
                        }
 
                        postfix[j] = pop(&s);
                        j++;
                    }
 
                    push(&s, ch);  // push ch to stack
                }
            }
        }
    }
 
    while (isEmpty(s) == 0)  // check if stack is empty
    {
        postfix[j] = pop(&s);
        j++;
    }
 
    postfix[j] = '\0';
}

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getPrecedence()

int getPrecedence	(	char	op1,
		char	op2
	)

getPrecedence function returns the precedence after comparing two operators passed as parameter.

Parameters

op1	: first operator
op2	: second operator

Returns

1 or 0 on exit

{
    if (op2 == '$')
    {
        return 0;
    }
    else if (op1 == '$')
    {
        return 1;
    }
    else if (op2 == '*' || op2 == '/' || op2 == '%')
    {
        return 0;
    }
    else if (op1 == '*' || op1 == '/' || op1 == '%')
    {
        return 1;
    }
    else if (op2 == '+' || op2 == '-')
    {
        return 0;
    }
    else
    {
        return 1;
    }
}

isEmpty()

int isEmpty

(

struct Stack

s

)

isEmpty function

Parameters

s	: it is the object reference of stack

Returns

1 or 0 on exit

{
    if (s.tos == -1)  // check if stack is empty
    {
        return 1;  // return for true result
    }
    else
    {
        return 0;  // return for false result
    }
}

isOprnd()

int isOprnd

(

char

ch

)

isOprnd function

Parameters

ch	: this is the element from the infix array

Returns

1 or 0 on exit

{
    if ((ch >= 65 && ch <= 90) ||
        (ch >= 97 && ch <= 122) ||  // check if ch is an operator or
        (ch >= 48 && ch <= 57))     // operand using ASCII values
    {
        return 1;  // return for true result
    }
    else
    {
        return 0;  // return for false result
    }
}

main()

int main

(

void

)

main function

Returns

0 on exit

{
    char infix[20], postfix[20];  // initialize empty infix and postfix array
 
    printf("Enter infix expression: ");  // example : A+B-C*D/E$F
    scanf("%s", infix);                  // get values for infix array
 
    convert(infix, postfix);
    printf("Postfix expression is %s", postfix);  // output : AB+CD*EF$/-
 
    return 0;
}

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pop()

int pop

(

struct Stack *

p

)

pop function

Parameters

*p	: used as a pointer variable of stack

Returns

x or \0 on exit

{
    char x;
 
    if (p->tos == -1)
    {
        printf("Stack Underflow!");
        return '\0';
    }
 
    x = p->arr[p->tos];  // assign the value of stack at index tos to x
    p->tos -= 1;         // decrement tos
 
    return x;
}

push()

void push	(	struct Stack *	p,
		char	x
	)

push function

Parameters

*p	: used as a pointer variable of stack
x	: char to be pushed in stack

Returns

void

{
    if (p->tos == 9)  // check if stack has reached its max limit
    {
        printf("Stack Overflow!");
        return;
    }
 
    p->tos += 1;         // increment tos
    p->arr[p->tos] = x;  // assign char x to index of stack pointed by tos
}

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