Programming Tutorials

Infix to Prefix And Postfix in C

By: Prachi in C Tutorials on 2009-03-21  

This is a sample program that converts Infix to Prefix and Postfix in C.

                                                        
#include <stdio.h>
#include <conio.h>
#include <string.h>
#define MAX 15
#define true 1
#define false 0

/*Structure Decvlaration*/
typedef struct
{
    char data[MAX];
    char top;
} STK;

/*Function Declarations*/
void input(char str[]);
void intopre(char str1[], char pre[]);
void intopost(char str1[], char post[]);
int isoperand(char sym);
int prcd(char sym);
void push(STK *s1, char elem);
int pop(STK *s1);
int empty(STK *s2);
int full(STK *s2);
void dis(char str[]);

void main()
{
    STK s;
    int cs, ans;
    char str[MAX], pre[MAX], post[MAX];
    clrscr();
    do /*Using Do-while Loop*/
    {
        clrscr();
        printf("-----Program for Expressions-----");
        printf("Input The String:");
        printf("MENU:");
        printf("1.Infix to Prefix");
        printf("2.Infix to Postfix");
        printf("3.Exit");
        cs = getche();

        switch (cs) /*Using Switch Case*/
        {
        case 1:
            intopre(str, pre);
            break;
        case 2:
            intopost(str, post);
            break;
        case 3:
            break;
        default:
            printf("Enter a Valid Choise!"); /*Default Case*/
            break;
        }
        printf("Do you wish to Continue?(y/n)");
        ans = getche();
    } while (ans == 'y' || ans == 'Y'); /*Condition for Do-while loop*/

    getch();
}

/**************************************************/
/*To Input String*/
/**************************************************/
void input(char str)
{
    printf("Enter the Infix String:");
    scanf("%s", str);
}

/**************************************************/
/*To Covert Infix To Prefix*/
/**************************************************/
void intopre(STK s1, char str1[], char pre[])
{
    int len, flag;
    len = strlen(str1);
    int check = 0, cnt = len - 1, pos = 0;
    char elem;

    while (cnt >= 0) /*while condition*/
    {
        flag = 0;
        if (isoperand(str1[cnt])) /*Checking for Operand*/
        {
            printf("%c", str1[cnt]);
            cnt--;
            pos++;
        }
        else
        {
            check = prcd(str1[cnt]);
            while (check == false)
            {
                pre[pos] = str1[cnt];
                flag = 1;
                pos++;
                cnt--;
            }
            if (flag == 0)
            {
                elem = pop(&s1);
                printf("%c", elem);
            }
        }
    }
}

/**************************************************/
/*To Convert Infix To Postfix*/
/**************************************************/
void intopost(STK s1, char str1[], char post[])
{
    int len;
    len = strlen(str1);
    int check = 0, cnt = len - 1, pos = 0;
}

/**************************************************/
/*To Check For Operand*/
/**************************************************/
int isoperand(char sym)
{
    if ('A' < sym < 'Z' || 'a' < sym < 'z')
        return (true);
    return (false);
}

/**************************************************/
/*To Check The Precedence*/
/**************************************************/
int prcd(char sym)
{
}

/**************************************************/
/*To Display String*/
/**************************************************/
void dis(char str[])
{
}

/******************************************/
/*Push Function Definition*/
/******************************************/
void push(STK *s1, char elem)
{
    if (!full(s1))
    {
        s1->top++;                /*Incrementing top*/
        s1->data[s1->top] = elem; /*Storing element*/
    }
    else
        printf("Stack is Full!");
}

/******************************************/
/*Full Function Definition*/
/******************************************/
int full(STK *s2)
{
    if (s2->top == MAX) /*Condition for Full*/
        return (true);
    return (false);
}

/******************************************/
/*Pop Function Definition*/
/******************************************/
int pop(STK *s1)
{
    char elem;
    if (!empty(s1))
    {
        elem = s1->data[s1->top]; /*Storing top stack element in elem*/
        s1->top--;                /*Decrementing top*/
        return (elem);
    }
    return (false);
}

/******************************************/
/*Empty Function Definition*/
/******************************************/
int empty(STK *s2)
{
    if (s2->top == -1) /*Condition For Empty*/
        return (true);
    return (false);
}