Remove spaces from a string in C++

Understanding String Manipulation

Removing spaces from a string means eliminating all whitespace characters.

We will explore three different methods to achieve this in C++.

Method 1: Using a Loop

This method iterates through the string and copies only non-space characters.

#include <iostream>
using namespace std;

void removeSpaces(string &str) {
    int count = 0;
    for (int i = 0; i < str.length(); i++)
        if (str[i] != ' ')
            str[count++] = str[i];
    str.resize(count);
}

int main() {
    string str = "Hello World!";
    removeSpaces(str);
    cout << "Filtered String: " << str;
    return 0;
}
            

Method 2: Using Recursion

This method removes spaces recursively.

#include <iostream>
using namespace std;

void removeSpacesRecursive(string &str, int index, int count) {
    if (index == str.length()) {
        str.resize(count);
        return;
    }
    if (str[index] != ' ')
        str[count++] = str[index];
    removeSpacesRecursive(str, index + 1, count);
}

int main() {
    string str = "C++ programming";
    removeSpacesRecursive(str, 0, 0);
    cout << "Filtered String: " << str;
    return 0;
}
            

Method 3: Using Pointers

This method uses pointers to remove spaces efficiently.

#include <iostream>
using namespace std;

void removeSpacesPointer(string &str) {
    char *i = &str[0], *j = &str[0];
    while (*i) {
        if (*i != ' ')
            *j++ = *i;
        i++;
    }
    str.resize(j - &str[0]);
}

int main() {
    string str = "Remove spaces";
    removeSpacesPointer(str);
    cout << "Filtered String: " << str;
    return 0;
}