Remove Consecutive Duplicates Recursively giving infinite recursion

Not a homework question.
I am self learning.
I have to remove consecutive characters in a string by recursion. However the program I made is not working for inputs containing duplicates. It is goining in infinite recursion and hence gives segmentation fault. However it is working for inputs which doesn't have consecutive duplicates in them. I have tried debugging in Eclipse Ide but things get weird when I debug. (I know how to debug) but I can't figure out the things are different when I debug and when I run. I will give you example after my code.

#include <iostream>
#include <cstring>
using namespace std;

void removeConsecutiveDuplicates(char *input) {
int l = strlen(input);
if(l == 0) {
return;
}
if(input[0] != input[1]) {
removeConsecutiveDuplicates(input+1);
return;
}
int i = 1;
for(; input[i] != ''; ++i) {
input[i-1] = input[i];
}
input[i] = '';
removeConsecutiveDuplicates(input);
}
int main(void) {
char ch[1000];
cin >> ch;
cout<<"The String Before Removing Duplicates : "<<ch<<endl;
removeConsecutiveDuplicates(ch);
cout<<"The String After Removing Duplicates : "<<ch<<endl;
return 0;
}


When I am debugging this code I and seeing the variable l value it is 16. This doesn't happen while running. What I am missing here?

std::string

char ch[1000]

string text; cin >> text; cout << "Before : " << text << "n"; text.erase(std::unique(text.begin(), text.end()), text.end()); cout << "After : " << text << "n";

*std::unique(input, input + strlen(input)) = '';

3 Answers
3

This line :

input[i] = '';


doesn't do anything (input[i] already has that value, because that was the end condition for the loop). You then call the removeConsecutiveDuplicates function recursively, but the length of the string is still the same, so you'll keep making recursive calls until a stack overflow happens.

input[i]

removeConsecutiveDuplicates

Instead, you need to make the string length smaller :

input[i - 1] = '';


to avoid this infinite recursion.

To pass your self-assigned homework problem :), explain why the following line never has any effect in your code:

input[i] = '';


In your function, change this:

input[i] = '';


to this:

input[i-1] = '';


since you have chopped away a character, thus you should decrease the size of your string.

Without that, you wouldn't reduce the size, thus looping over and over again the same size, without it changing, would result in an infinite loop (since the size wouldn't change).

I suggest you use an std::string next time, since this is C++.

std::string

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