Input and output using cin and cout in C++ - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this C++ code?

Consider the following code snippet. What will be printed when the input is 5 10?

C++

#include <iostream>
using namespace std;

int main() {
    int a, b;
    cin >> a >> b;
    cout << a + b << endl;
    return 0;
}

A 5 10

B 510

C 15

D Compilation error

💡 Hint

Remember that operator >> reads integers and skips spaces.

The code reads two integers 5 and 10, then outputs their sum, which is 15.

❓ Predict Output

intermediate

What does this code print given input "Hello World"?

Look at this code. What will it output if the user types Hello World?

C++

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

int main() {
    string s;
    cin >> s;
    cout << s << endl;
    return 0;
}

A Hello World

B Hello

C World

D Compilation error

💡 Hint

cin >> string reads only until the first space.

cin >> s reads only the first word 'Hello' and stops at the space.

❓ Predict Output

advanced

What is the output of this code reading multiple inputs?

Given the input 3 4 5, what will this program print?

C++

#include <iostream>
using namespace std;

int main() {
    int x, y, z;
    cin >> x >> y >> z;
    cout << x << y << z << endl;
    return 0;
}

A 345

B 3 4 5

C 12

D Compilation error

💡 Hint

cout with multiple << outputs values without spaces.

The program prints the three integers concatenated without spaces: 345.

❓ Predict Output

advanced

What error does this code cause?

What error will this code produce when run?

C++

#include <iostream>
using namespace std;

int main() {
    int a;
    cout << "Enter a number: ";
    cin >> a;
    cout << "You entered: " << b << endl;
    return 0;
}

A Compilation error: 'b' was not declared

B Runtime error: segmentation fault

C Outputs the entered number

D No output

💡 Hint

Check variable names carefully.

Variable 'b' is used but never declared, causing a compilation error.

🧠 Conceptual

expert

What is the output of this code with mixed input types?

Given the input 42 hello 3.14, what will this program output?

C++

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

int main() {
    int i;
    string s;
    double d;
    cin >> i >> s >> d;
    cout << s << " " << i << " " << d << endl;
    return 0;
}

A Compilation error

B 42 hello 3.14

C 3.14 42 hello

D hello 42 3.14

💡 Hint

cin reads inputs in order and cout prints in the order given.

cin reads 42 into i, 'hello' into s, and 3.14 into d. cout prints s, i, d in that order.