Multiple input and output in C++ - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of function with multiple inputs and outputs using references

What is the output of the following C++ program?

C++

#include <iostream>
using namespace std;

void updateValues(int a, int& b, int& c) {
    a = a + 10;
    b = b + 20;
    c = c + 30;
}

int main() {
    int x = 1, y = 2, z = 3;
    updateValues(x, y, z);
    cout << x << " " << y << " " << z << endl;
    return 0;
}

A 1 22 33

B 11 22 33

C 11 2 3

D 1 2 3

💡 Hint

Remember that only variables passed by reference can be changed outside the function.

The variable 'a' is passed by value, so changes inside the function do not affect 'x'. Variables 'b' and 'c' are passed by reference, so their values are updated.

❓ Predict Output

intermediate

Output of function returning multiple values via pointers

What will be printed by this C++ program?

C++

#include <iostream>
using namespace std;

void compute(int a, int b, int* sum, int* product) {
    *sum = a + b;
    *product = a * b;
}

int main() {
    int x = 4, y = 5, s = 0, p = 0;
    compute(x, y, &s, &p);
    cout << s << " " << p << endl;
    return 0;
}

A 45 9

B 9 9

C 9 20

D 20 9

💡 Hint

Pointers allow the function to modify variables outside its scope.

The function sets '*sum' to 4+5=9 and '*product' to 4*5=20, so the output is '9 20'.

🔧 Debug

advanced

Identify the error in multiple output function using references

This code is intended to swap two integers using references. What is the output of this C++ program?

C++

#include <iostream>
using namespace std;

void swap(int a, int b) {
    int temp = a;
    a = b;
    b = temp;
}

int main() {
    int x = 10, y = 20;
    swap(x, y);
    cout << x << " " << y << endl;
    return 0;
}

A Compilation error: missing & in function parameters

B Output: 10 20

C Output: 20 10

D Runtime error: segmentation fault

💡 Hint

Check how the function parameters are passed and if changes affect the original variables.

The function parameters are passed by value, so swapping inside the function does not affect 'x' and 'y'. The output remains '10 20'.

❓ Predict Output

advanced

Output of function returning multiple values using std::tuple

What is the output of this C++ program that returns multiple values using std::tuple?

C++

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

tuple<int, int> minMax(int a, int b) {
    if (a < b) return {a, b};
    else return {b, a};
}

int main() {
    int x = 7, y = 3;
    auto [minVal, maxVal] = minMax(x, y);
    cout << minVal << " " << maxVal << endl;
    return 0;
}

A 3 7

B 7 3

C 0 0

D Compilation error: structured bindings not supported

💡 Hint

Structured bindings unpack the tuple into variables.

The function returns the smaller and larger values correctly. Structured bindings assign them to minVal and maxVal.

🧠 Conceptual

expert

Understanding multiple output methods in C++ functions

Which of the following statements about returning multiple outputs from a C++ function is NOT true?

A Functions can only return one value directly, so multiple outputs need workarounds.

B Returning a std::tuple can return multiple values but requires unpacking by the caller.

C Using references as function parameters allows modifying variables outside the function.

D Using pointers as parameters is unsafe and always causes runtime errors.

💡 Hint

Think about pointer usage and safety in C++.

Pointers can be used safely if handled correctly. They do not always cause runtime errors.

Practice

1.

Which of the following statements correctly reads two integers a and b from the user in C++?

easy

A. std::cout >> a >> b;

B. std::cin << a << b;

C. std::cout << a << b;

D. std::cin >> a >> b;

Solution

1. Step 1: Understand input operator usage

   In C++, std::cin is used for input and the extraction operator >> reads values.

2. Step 2: Identify correct syntax for multiple inputs

   Using std::cin >> a >> b; reads two integers from the user correctly.

3. Final Answer:

   std::cin >> a >> b; -> Option D

4. Quick Check:

   Input uses std::cin with >> operator [OK]

Hint: Use std::cin with >> to read multiple inputs [OK]

Common Mistakes:

• Using << instead of >> for input
• Using std::cout for input
• Mixing input and output operators

2.

Which of the following lines correctly prints three variables x, y, and z separated by spaces in C++?

easy

A. std::cout << x << ' ' << y << ' ' << z;

B. std::cout << x, y, z;

C. std::cout >> x >> y >> z;

D. std::cin << x << y << z;

Solution

1. Step 1: Understand output operator usage

   In C++, std::cout is used for output and the insertion operator << prints values.

2. Step 2: Print multiple variables with spaces

   Using std::cout << x << ' ' << y << ' ' << z; prints variables separated by spaces correctly.

3. Final Answer:

   std::cout << x << ' ' << y << ' ' << z; -> Option A

4. Quick Check:

   Output uses std::cout with << and spaces [OK]

Hint: Use std::cout with << and spaces to print multiple values [OK]

Common Mistakes:

• Using commas instead of << for output
• Using >> operator for output
• Using std::cin for output

3.

What is the output of the following C++ code if the user inputs 5 10?

int a, b;
std::cin >> a >> b;
std::cout << a + b << ' ' << a * b << std::endl;

medium

A. 15 50

B. 510

C. 5 10

D. Syntax Error

Solution

1. Step 1: Read input values

   The code reads two integers: a = 5 and b = 10 from user input.

2. Step 2: Calculate and print sum and product

   The output prints a + b = 15 and a * b = 50 separated by a space.

3. Final Answer:

   15 50 -> Option A

4. Quick Check:

   Sum and product printed with space [OK]

Hint: Add and multiply inputs, print with space [OK]

Common Mistakes:

• Concatenating numbers as strings
• Forgetting space between outputs
• Confusing input and output operators

4.

Identify the error in the following C++ code snippet:

int x, y;
std::cin << x << y;
std::cout << x << y;

medium

A. Missing semicolon after std::cin

B. >> used instead of << for output

C. << used instead of >> for input

D. Variables x and y not declared

Solution

1. Step 1: Check input operator usage

   Input uses std::cin with extraction operator >>, but code uses << which is wrong.

2. Step 2: Check output operator usage

   The code correctly uses std::cout with insertion operator <<.

3. Final Answer:

   << used instead of >> for input -> Option C

4. Quick Check:

   Input needs >> operator, not << [OK]

Hint: Input uses >>, output uses << operators [OK]

Common Mistakes:

• Swapping << and >> operators
• Confusing std::cin and std::cout
• Ignoring operator direction

5.

Given the following code, what will be the output if the user inputs 3 4 5?

int a, b, c;
std::cin >> a >> b >> c;
std::cout << a + b << ' ' << b + c << ' ' << a + c << std::endl;

medium

A. Runtime Error

B. 7 9 8

C. 3 4 5

D. 12 9 7

Solution

1. Step 1: Read three integers from input

   The variables are assigned as a=3, b=4, c=5 from user input.

2. Step 2: Calculate sums and print

   Prints a + b = 7, b + c = 9, and a + c = 8 separated by spaces.

3. Final Answer:

   7 9 8 -> Option B

4. Quick Check:

   Sum pairs printed correctly [OK]

Hint: Add pairs of inputs and print with spaces [OK]

Common Mistakes:

• Adding all three instead of pairs
• Mixing input order
• Forgetting spaces between outputs