C Program returning a series of question marks at the end or sometimes, returning nothing

Question

My program is supposed to erase /**/ comments, condense white spaces, and remove line splices of the input.

**edit: scroll down to problem update below.

Here is my code:

#include <stdio.h>

void ass(), f1(), f2(), f3();

int mainRunner();

int a, b;

int main() {
    ass();
    mainRunner();
}

void ass() {
    a = getchar();
    b = getchar();
}

int mainRunner() {
    while ( a != EOF ) {
        f1();
        f2();
        f3();
        putchar(a);
        a = b;
        b = getchar();
    }
}

// Removes Line Splices
void f1() {
    if ((a == '\\') && (b == '\n')) {
        a = getchar();
        b = getchar();
        mainRunner();
    }
}

//Removes Comments in the /*...*/ form
void f2() {
    if ((a == '/') && (b == '*')) {
        while ((a != '*') || (b != '/')) {
            a = b;
            b = getchar();
        }
        a = getchar();
        b = getchar();
        mainRunner();
    }
}

//Condenses White Spaces
void f3() {
    if ((a == ' ') && (b == ' ')) {
        a = b;
        b = getchar();
        mainRunner();
    }
}

When I run the testscript (testscript 1):

a b  c
d             e
f
g


hifealkfja;efa  faekjf;ale   feafaefa

This is returned

a b c
d e
f
g


hifealkfja;efa faekjf;ale feafaefa
????????????????

When I run this testscript (testscript 2):

start linesplice NOW!\
This should be connected with first line.Comment begins here:/*fjelajfal;efjael$
fe;ajfe;fe8/Comment Ends.
Series of 5 spaces between the letters:a     b
Series of 10 spaces between the letters:c          d
Increasing number of spaces between letters from 1 space:e f  g   h    i

Nothing happens and the command line cursor goes to the very left.

I appreciate any feedback, thanks. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Problem Update: Reduced the issue above by doing what chux suggested. Now I only have the question mark problem. I made a fix so that putchars wouldn't be waiting in the stack and output a whole bunch of EOFs at the end, but why are there still two question marks? Here's my new code:

#include <stdio.h>

void ass();

int mainRunner();

int a, b;

int main() {
    ass();
    mainRunner();
}

void ass() {
    a = getchar();
    b = getchar();
}

int mainRunner() {
    while ( a != EOF ) {
        // Removes Line Splices
        if ((a == '\\') && (b == '\n')) {
            a = getchar();
            b = getchar();
            mainRunner();
        }
        //Removes Comments in the /*...*/ form
        if ((a == '/') && (b == '*')) {
            while ((a != '*') || (b != '/')) {
                a = b;
                b = getchar();
            }
            a = getchar();
            b = getchar();
            mainRunner();
        }
        //Condenses White Spaces
        if ((a == ' ') && (b == ' ')) {
            a = b;
            b = getchar();
            mainRunner();
        }
        if (a == EOF) {
            break;
        }
        else {
            putchar(a);
            a = b;
            b = getchar();
        }
    }
}

When I run the second test script from above (with an asterisk added to end the comment), my program outputs:

start linesplice NOW!This should be connected with first line.Comment begins here:Comment Ends. Series of 5 spaces between the letters:a b Series of 10 spaces between the letters:c d Increasing number of spaces between letters from 1 space:e f g h i ??

Notice the two question marks at the end. Note: the program works fine for the first test script.

Answer 1

Given OP's first testscript:

The if in f1() is never true.

The if in f2() is never true.

f3() effectively recurses into itself via mainRunner() when multiple space are encountered. Upon seeing EOF, the recursion stops, and unwinds. mainRunner() performs putchar(a); with EOF in a with each unwinding.

---

Removing mainRunner(); in f1(), f2(), & f3() may help.

The test code has 1 + 13 + 1 + 2 sequences of 2 spaces. This causes 17 recursive calls. Upon unwinding putchar(EOF) is called 16 times creating the '?'.

---

In OP's 2nd testscript. f2() gets into an infinite loop with

while ((a != '*') || (b != '/')) {
  a = b;
  b = getchar();
}

as there is no escape should getchar() return EOF.