How do I replace two a's in a string with an '*'

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Hey guys so for my assignment I have to replace two a's with an '*' from a string of unknown input length in C. The challenge is I am only allowed to use the getchar() and the putchar() function.
With an array it would have been easier but I am not even allowed to use that.

What I have tried:

C++

#include <stdio.h>

int ch;

int main()
{
    while ((ch = getchar()) !=EOF && ch != '\n'  ) { 
        if(ch=='a'){
            if(ch=='a'){
                ch='*';
            }
        }
        putchar(ch);
    }
    putchar('\n');
    return 0;
}

Posted 13-Apr-18 12:03pm

Member 13778651

Updated 13-Apr-18 15:23pm

Rick York

v2

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Patrice T · Answer 1 · 2018-04-13T15:24:00

This code is wrong and need rewrite

C++

if(ch=='a'){
    if(ch=='a'){
        ch='*';
    }
}
putchar(ch);

As per assignment, when you encounter an 'a', you know what to do only when you know the next letter.
You need a variable to tell you if you have an 'a' on hold or not.
And you need to adapt the code to handle if a 'a' is on hold or not.
The code will look like:

C++

if(ch=='a'){
  if (a 'a' is on hold) {
    putchar('*');
    reset number of 'a' in hold
  }
  else {
    add a 'a' in hold
  }
}
else {
  if (a 'a' is on hold) {
    ...
  }
  ...
}

[Update]

Quote:
could you please explain what you mean by "in hold" and "on hold" english is not my first language

Sample input

Input   on Hold   Output
  b                 b
  a       a
  n                 a n
  a       a
  a                 *
  a       a
  n                 a n
  a       a
  \n                a \n

You can translate 'on hold' as waiting for next input. Said otherwise: you don't know what to do with a 'a' until you know if there is a second 'a'.