// C++ program to implement custom trim() function
#include <iostream>
using namespace std;

// Function to in-place trim all spaces in the
// string such that all words should contain only
// a single space between them.
void removeSpaces(string &str)
{
	// n is length of the original string
	int n = str.length();

	// i points to next position to be filled in
	// output string/ j points to next character
	// in the original string
	int i = 0, j = -1;

	// flag that sets to true is space is found
	bool spaceFound = false;

	// Handles leading spaces
	while (++j < n && str[j] == ' ');

	// read all characters of original string
	while (j < n)
	{
		// if current characters is non-space
		if (str[j] != ' ')
		{
			// remove preceding spaces before dot,
			// comma & question mark
			if ((str[j] == '.' || str[j] == ',' ||
				str[j] == '?') && i - 1 >= 0 &&
				str[i - 1] == ' ')
				str[i - 1] = str[j++];

			else
				// copy current character at index i
				// and increment both i and j
				str[i++] = str[j++];

			// set space flag to false when any
			// non-space character is found
			spaceFound = false;
		}
		// if current character is a space
		else if (str[j++] == ' ')
		{
			// If space is encountered for the first
			// time after a word, put one space in the
			// output and set space flag to true
			if (!spaceFound)
			{
				str[i++] = ' ';
				spaceFound = true;
			}
		}
	}

	// Remove trailing spaces
	if (i <= 1)
		str.erase(str.begin() + i, str.end());
	else
		str.erase(str.begin() + i - 1, str.end());
}

// Driver Code
int main()
{
	string str = " Hello Geeks . Welcome to"
				" GeeksforGeeks . ";

	removeSpaces(str);

	cout << str;

	return 0;
}
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#include <iostream>
#include <string>
using namespace std;

int main() 
{
    string name;
    cout << "Enter name:";
    getline (cin, name);
    cout << "Hello " << name;
    return 0;
}

About C++

C++ is a widely used middle-level programming language.

  • Supports different platforms like Windows, various Linux flavours, MacOS etc
  • C++ supports OOPS concepts like Inheritance, Polymorphism, Encapsulation and Abstraction.
  • Case-sensitive
  • C++ is a compiler based language
  • C++ supports structured programming language
  • C++ provides alot of inbuilt functions and also supports dynamic memory allocation.
  • Like C, C++ also allows you to play with memory using Pointers.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition If-Else is used.

if(conditional-expression) {
   //code
}
else {
   //code
}

You can also use if-else for nested Ifs and If-Else-If ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to If-Else-If ladder.

switch(conditional-expression){    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
......    
    
default:     
 code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  //code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while (condition) {  
// code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {  
 // code 
} while (condition);

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity. Function gets run only when it is called.

How to declare a Function:

return_type function_name(parameters);

How to call a Function:

function_name (parameters)

How to define a Function:

return_type function_name(parameters) {  
 // code
}