C Program to convert Prefix into INFIX

Write a C Program to convert Prefix into INFIX Expression.Here’s a Simple Program To Convert Prefix To Infix Notation using Stack in C Programming Language.

The Prefix notation is also known as Polish Notation.

Prefix To Infix Example :

Prefix String : : + A B C

Infix String  : : ((A+B)C)

Algorithm :

1. The Reversed Prefix Expression is pushed on the Stack.
2. If the Stack is not Empty, then Pop the elements from the Stack
3. If the popped character is an Operator
   1. Input Opening Parantheses ‘(‘ and print it on the console.
   2. Display popped character from the Stack.
   3. Input Closing Parantheses ‘)’ and print it on the console.
4. If the popped character is an empty space, then print it on the console.
5. Repeat the steps till the Prefix expression is not scanned completely.

Below is the source code for C Program to convert Prefix into INFIX Expression which is successfully compiled and run on Windows System to produce desired output as shown below :

SOURCE CODE : :

#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <conio.h>
char opnds[50][80],oprs[50];
int  topr=-1,topd=-1;
pushd(char *opnd)
{
    strcpy(opnds[++topd],opnd);
}
char *popd()
{
    return(opnds[topd--]);
}

pushr(char opr)
{
    oprs[++topr]=opr;
}
char popr()
{
    return(oprs[topr--]);
}
int empty(int t)
{
    if( t == 0) return(1);
    return(0);
}

void main()
{
    char prfx[50],ch,str[50],opnd1[50],opnd2[50],opr[2];
    int i=0,k=0,opndcnt=0;

    printf("Give an Expression = ");
    gets(prfx);
    printf(" Given Prefix Expression : %s\n",prfx);
    while( (ch=prfx[i++]) != '\0')
    {
        if(isalnum(ch))
        {
            str[0]=ch; str[1]='\0';
            pushd(str); opndcnt++;
            if(opndcnt >= 2)
            {
                strcpy(opnd2,popd());
                strcpy(opnd1,popd());
                strcpy(str,"(");
                strcat(str,opnd1);
                ch=popr();
                opr[0]=ch;opr[1]='\0';
                strcat(str,opr);
                strcat(str,opnd2);
                strcat(str,")");
                pushd(str);
                opndcnt-=1;
            }
        }
        else
        {
            pushr(ch);
            if(opndcnt==1)opndcnt=0;  /* operator followed by single operand*/
        }
    }
    if(!empty(topd))
    {
        strcpy(opnd2,popd());
        strcpy(opnd1,popd());
        strcpy(str,"(");
        strcat(str,opnd1);
        ch=popr();
        opr[0]=ch;opr[1]='\0';
        strcat(str,opr);
        strcat(str,opnd2);
        strcat(str,")");
        pushd(str);
    }
    printf(" Infix Expression: ");
    puts(opnds[topd]);
    getch();
}

OUTPUT : :

FIRST RUN ::

Give an Expression = +++++abcde
 Given Prefix Expression : +++++abcde
 Infix Expression: ((((a+b)+c)+d)+e)


SECOND RUN ::

Give an Expression = +-435
 Given Prefix Expression : +-435
 Infix Expression: ((4-3)+5)


THIRD RUN  ::

Give an Expression = ++a*bcd
 Given Prefix Expression : ++a*bcd
 Infix Expression: (a+((b*c)+d))

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