Input and output using cin and cout in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to read an integer from the user using cin.

C++

#include <iostream>
using namespace std;

int main() {
    int number;
    cin [1] number;
    cout << "You entered: " << number << endl;
    return 0;
}

Drag options to blanks, or click blank then click option'

A>>

B<<

C>>=

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using << instead of >> with cin causes a syntax error.

Using == is a comparison, not input.

Using >>= is a bitwise operator, not for input.

The extraction operator for input with cin is >>. It reads data from the user into the variable.

2fill in blank

medium

Complete the code to print a message to the console using cout.

C++

#include <iostream>
using namespace std;

int main() {
    cout [1] "Hello, world!" << endl;
    return 0;
}

Drag options to blanks, or click blank then click option'

A>>

B<<

C==

D>>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using >> instead of << with cout causes a syntax error.

Using == is a comparison, not output.

Using >>= is a bitwise operator, not for output.

The insertion operator for output with cout is <<. It sends data to the console.

3fill in blank

hard

Fix the error in the code to correctly read a floating-point number using cin.

C++

#include <iostream>
using namespace std;

int main() {
    float value;
    cin [1] value;
    cout << "Value: " << value << endl;
    return 0;
}

Drag options to blanks, or click blank then click option'

A<<

B=>

C==

D>>

Attempts:

3 left

💡 Hint

Common Mistakes

Using << instead of >> with cin.

Using == or => which are not input operators.

To read input with cin, use the extraction operator >>. Using << or other operators causes errors.

4fill in blank

hard

Fill both blanks to create a program that reads two integers and prints their sum.

C++

#include <iostream>
using namespace std;

int main() {
    int a, b;
    cin [1] a >> b;
    cout [2] "Sum: " << (a + b) << endl;
    return 0;
}

Drag options to blanks, or click blank then click option'

A>>

B<<

C==

D>>=

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up << and >> operators.

Using == instead of input/output operators.

Use >> to read input with cin and << to output with cout.

5fill in blank

hard

Fill all three blanks to read a string and an integer, then print them in a sentence.

C++

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

int main() {
    string name;
    int age;
    cin [1] name >> age;
    cout [2] "Name: " << [3] << ", Age: " << age << endl;
    return 0;
}

Drag options to blanks, or click blank then click option'

A>>

Bname

C<<

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using == instead of input/output operators.

Forgetting to print the variable name.

Mixing up << and >> operators.

Use >> to read input, << to output, and the variable name to print the string.

Practice

1. What does cin do in a C++ program?

easy

A. It declares a variable.

B. It prints output to the screen.

C. It reads input from the user.

D. It ends the program.

Solution

1. Step 1: Understand the role of cin

   cin is used to get input from the user during program execution.

2. Step 2: Differentiate from cout

   cout is used to show output, not input.

3. Final Answer:

   It reads input from the user. -> Option C

4. Quick Check:

   cin = input [OK]

Hint: Remember: cin reads input, cout shows output [OK]

Common Mistakes:

• Confusing cin with cout
• Thinking cin prints output
• Mixing input and output operators

2. Which of the following is the correct syntax to read an integer variable num from the user?

easy

A. cout >> num;

B. cout << num;

C. cin << num;

D. cin >> num;

Solution

1. Step 1: Identify input operator usage

   To read input, use cin with the extraction operator >>.

2. Step 2: Check each option

   cin >> num; is the correct syntax for input. Options using cout are for output, not input. The option with cin << num; uses the wrong operator <<.

3. Final Answer:

   cin >> num; -> Option D

4. Quick Check:

   Input syntax = cin >> variable [OK]

Hint: Use >> with cin to get input [OK]

Common Mistakes:

• Using << with cin instead of >>
• Using cout instead of cin for input
• Forgetting semicolon

3. What will be the output of this code if the user inputs 5?

int num;
std::cin >> num;
std::cout << num + 3;

medium

A. 5

B. 8

C. 3

D. Error

Solution

1. Step 1: Read input value

   The user inputs 5, so num becomes 5.

2. Step 2: Calculate output expression

   The program outputs num + 3 which is 5 + 3 = 8.

3. Final Answer:

   8 -> Option B

4. Quick Check:

   5 + 3 = 8 [OK]

Hint: Add 3 to input number before printing [OK]

Common Mistakes:

• Printing input without adding 3
• Confusing input and output
• Expecting error due to input

4. What is wrong with this code snippet?

int age;
std::cin << age;
std::cout >> age;

medium

A. The operators with cin and cout are reversed.

B. Variables are not declared.

C. Missing semicolons.

D. No errors.

Solution

1. Step 1: Check operators used with cin and cout

   cin should use >> to get input, but code uses <<. Similarly, cout should use << to output, but code uses >>.

2. Step 2: Confirm variable declaration and semicolons

   Variable age is declared and semicolons are present, so no issues there.

3. Final Answer:

   The operators with cin and cout are reversed. -> Option A

4. Quick Check:

   cin >> input, cout << output [OK]

Hint: cin uses >>, cout uses << operators [OK]

Common Mistakes:

• Using << with cin
• Using >> with cout
• Ignoring operator direction

5. You want to read two integers from the user and print their sum. Which code correctly does this?

hard

A. int a, b;
cin >> a >> b;
cout << a + b;

B. int a, b;
cin << a << b;
cout >> a + b;

C. int a, b;
cin >> a;
cin << b;
cout << a + b;

D. int a, b;
cout >> a >> b;
cin << a + b;

Solution

1. Step 1: Check input statements

   int a, b; cin >> a >> b; cout << a + b; uses cin >> a >> b; which correctly reads two integers.

2. Step 2: Check output statement

   int a, b; cin >> a >> b; cout << a + b; uses cout << a + b; which correctly prints the sum.

3. Final Answer:

   int a, b; cin >> a >> b; cout << a + b; -> Option A

4. Quick Check:

   Use >> with cin and << with cout [OK]

Hint: Chain inputs with >> and output with << [OK]

Common Mistakes:

• Using << with cin or >> with cout
• Separating input into wrong operators
• Mixing input and output streams