cin in C++

cin is a predefined object in C++ used to accept input from the standard input stream (stdin). It works with the extraction operator (>>) to read data entered by the user and store it in variables.

• Used to read input from the keyboard during program execution
• Works with the extraction operator (>>) to extract data from the input stream
• Supports reading different data types such as integers, characters, strings, and floating-point values

#include <iostream>
using namespace std;

int main() {
  
  	// Variable to store data given by cin
    int a;

    // Take input using cin
    cin >> a;

    cout << a;
    return 0;
}

Input

10

Output

10

Syntax of cin

cin >> var_name;

Here,

• cin is the standard input stream object
• >>: It is the extraction operator to extract data from cin.
• var_name: It is a variable that will store the input data provided by the user.

Note: cin is initialized when the program starts to make sure it is ready for input operations. It is also linked to cout to ensure that any buffered output is flushed before cin reads from the input stream.

Examples of cin

The following examples demonstrate different ways of using `cin` for input operations in C++.

Example: Taking Text from User Input

#include <iostream>
using namespace std;

int main() {
  
  	// Variable to store data given by cin
    string s;

    // Take input using cin
    cin >> s;

    // Print output
    cout << s;
    return 0;
}

Input

Welcome to GeeksforGeeks

Output

Welcome

Explanation

• cin reads input until the first whitespace character is encountered
• Only the word "Welcome" is stored in the string variable
• The remaining words are not read by this input operation

Example: Taking Multiple Inputs Using the Extraction Operator(>>) with cin

#include <iostream>
using namespace std;

int main() {
    string name;
    int age;

    // Take multiple input using cin
    cin >> name >> age;

    cout << "Name : " << name << endl;
    cout << "Age : " << age << endl;

    return 0;
}

 
Input

ABC 13

Output

Name : ABC
Age : 13

Explanation

• Multiple values can be read using a single cin statement
• Each value is extracted sequentially from the input stream
• The first value is stored in name and the second value is stored in age

cin Member Functions of cin

The cin object provides several member functions that offer greater control over input operations.

cin.get()

It reads an input character and stores it in a variable.

#include <iostream>
using namespace std;

// Driver Code
int main()
{
    char ch[30];
    cin.get(ch, 25);

    // Print ch
    cout << ch;
}

Input

Welcome to GFG

Output

Welcome to GFG

Explanation

• cin.get() reads characters from the input stream, including whitespace
• It stores the extracted characters in the specified character array
• Input continues until the specified limit is reached or a delimiter is encountered

cin.getline()

It reads a stream of characters of given length N into the string buffer. It stops when it has read (N - 1) characters or it finds the end of the file or newline character(\n).

#include <iostream>
using namespace std;

int main() {
    char name[5];

    // Reads stream of 3 characters
    cin.getline(name, 3);

    // Print output
    cout << name << endl;

    return 0;
}

Input

Geeks

Output

Ge

Explanation

• cin.getline() reads an entire line of input, including spaces
• Reading stops when the specified character limit is reached
• It also stops when a newline character is encountered

cin.read()

It reads a stream of characters of given length N.

#include <iostream>
using namespace std;

int main() {
    char gfg[20];

    // Reads stream of characters
    cin.read(gfg, 10);

    // Print output
    cout << gfg << endl;

    return 0;
}

Input

Welcome to GFG

Output

Welcome to

Explanation

• cin.read() reads a fixed number of characters from the input stream
• It does not stop when whitespace characters are encountered
• The specified number of characters are copied into the buffer

cin.ignore()

It ignores or clears one or more characters from the input buffer.

#include <iostream>
#include <ios>
#include <limits>
using namespace std;

int main() {
    int x;
    char str[80];
    cout << "Enter a number and string:\n";
    cin >> x;

    // clear buffer before taking
    // new line
    cin.ignore(numeric_limits<streamsize>::max(), '\n');

    // Input a string
    cin.getline(str, 80);
    cout << "You have entered:\n";
    cout << x << endl;
    cout << str << endl;

    return 0;
}

Input

Enter a number and string:
8
Welcome to GFG

Output

You have entered:
8
Welcome to GFG

Explanation

• After reading an integer, the Enter key leaves a newline character in the input buffer
• If getline() is called immediately, it may read this newline character instead of actual input
• cin.ignore() removes the leftover newline character from the buffer
• This ensures that the subsequent getline() call works correctly

The below table lists some commonly used member functions of cin in C++: