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Write a C program to convert a polish notation to reverse polish notation.

Mumbai University > COMPS > Sem 3 > Data Structures

Marks: 10 M

Year: Dec 2014

1 Answer
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Polish notation is another name for Prefix notation. Reverse Polish notation means postfix expression. So, here we need to convert prefix to postfix notation.

#include<stdio.h>
#include<string.h>
void push(char item[], int *top, char s[][20])
{
    *top = *top + 1;
    strcpy(s[*top], item);
}
void *pop(int *top, char s[][20])
{
    char *item;
    item = s[*top];
    *top = *top - 1;
    return item;
}
void pre_post(char prefix[], char postfix[])
{
    char s[20][20];
    int top, i;
    char symbol, temp[2];
    char *op1, *op2;
    top = -1;
    strrev(prefix);
    for (i = 0;i < strlen(prefix);i++)
    {
        symbol = prefix[i];
        temp[0] = symbol;
        temp[1] = '\0';
        switch (symbol)
        {
        case '+':
        case '-':
        case '*':
        case '/':
        case '^':
            op1 = pop(&top, s);
            op2 = pop(&top, s);
            strcpy(postfix, op1);

            strcat(postfix, op2);
            strcat(postfix, temp);
            push(postfix, &top, s);
            break;
        default:
            push(temp, &top, s);
        }
    }
}
int main()
{
    char prefix[20];
    char postfix[20];
    printf("\n\n Enter the prefix expression \n\n");
    scanf("%s", prefix);
    pre_post(prefix, postfix);
    printf("\n\n The postfix expression is %s \n\n", postfix);
    return 0;
}
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