Question

I had to build a C program which convert’s infix notation into postfix notation using STACK. That went well and it’s working in some way. It was long ago when I used last time C language so I’m probably dont use char[] variables very well.

So problem is that when I give input like this :

A+B*(C*E-D)

My program returns this :

ABCE*D-*+ĚĚĚĚĚĚĚĚĚĚĚ

So as you see my program did postfix conversion very well but I have bunch of “garbage” chars at my result (ĚĚĚĚĚĚĚĚĚĚĚ).

Here is snippet of my code (only part that I think is not correct, maybe something with char[] and way how I assing value to postfix[] variable:

int main()
{
    char infix[20], postfix[20];
    int len, tip, i, p=0;

    STACK pom;
    MAKE_NULL(&pom);

    printf ("Unesi izraz.\n");
    scanf ("%s", infix);

    len = strlen(infix);

    for(i=0; i<len; i++)
    {
        tip = nadi_tip(infix[i]);

        if (tip == Lijeva)
        {
            PUSH (infix[i], &pom);
        }

        if (tip == Operand)
        {
            postfix[p] = infix[i];
            p++;
        }

        if (tip == Desna)
        {
            while (!EMPTY(pom) && (TOP(pom)!= '('))
              {
                postfix[p++] = TOP(pom);
                POP (&pom);
              }
            POP (&pom);
        }

        if (tip == Operator)
        {
            while (!EMPTY(pom) && TOP(pom)!= '(')
             {
                if(prioritet(infix[i]) <= prioritet(TOP(pom)))
                {
                  postfix[p++] = TOP(pom);
                  POP (&pom);
                }
                else break;
             }
             PUSH(infix[i], &pom);
        }
    }
 while (EMPTY(pom) != 1)
 {
    postfix[p++] = TOP(pom);
    POP(&pom);
 }

 printf("Izlaz: %s", postfix);
 return 0;

}

infix[] is my input and postfix[] is my output. What did I do wrong I why am I having ĚĚĚĚĚĚĚĚĚĚĚ characters. Thank you in advance!

Answer 1

It looks like you don’t have a NUL terminator on your postfix string. You could either change the definition to char postfix[20] = {0};, or you just before the printf, you could add postfix[p] = '\0';