Answer to Question #294086 in C++ for Roe

Question

Write a program which converts infix expression entered by the user into postfix expression.

Requirements:

Implement this using arrays

Make functions

No global decelerations

Run test in main

Answer 1

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <stdio.h>
#include <ctype.h>






void push(char elem , char *array , int & top)
{ 
    array[++top] = elem;
}


char pop( char* array, int& top)
{      
    return(array[top--]);
}


int pr(char symbol)
{ 


    if (symbol == '^')/* exponent operator, highest precedence*/
    {
        return(3);
    }
    else if (symbol == '*' || symbol == '/')
    {
        return(2);
    }
    else if (symbol == '+' || symbol == '-')          /* lowest precedence */
    {
        return(1);
    }
    else
    {
        return(0);
    }
}
/* Main Program */
int main()
{
        
    const int SIZE = 100;
    char array[SIZE];
    int top = -1;      


    char infix[50], postfix[50], ch, elem;
    int i = 0, k = 0;
    printf("Enter Infix Expression : ");
    scanf("%s", infix);
    push('#' , array , top);
    while ((ch = infix[i++]) != '\0')
    {
        if (ch == '(') push(ch , array , top);
        else
            if (isalnum(ch)) postfix[k++] = ch;
            else
                if (ch == ')')
                {
                    while (array[top] != '(')
                        postfix[k++] = pop(array , top);
                    elem = pop(array , top); /* Remove ( */
                }
                else
                {       /* Operator */
                    while (pr(array[top]) >= pr(ch))
                        postfix[k++] = pop(array , top);
                    push(ch , array , top);
                }
    }
    while (array[top] != '#')     /* Pop from array till empty */
        postfix[k++] = pop(array , top);
    postfix[k] = '\0';          /* Make postfix as valid string */
    printf("\nPostfix Expression =  %s\n", postfix);
    system("pause");
    return 0;
}