Passing parameters by reference in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a function parameter that passes an integer by reference.

C++

void increment([1] int &num) {
    num++;
}

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Avolatile

Bconst

Csigned

Dunsigned

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting the & symbol to pass by reference

Using pointer syntax instead of reference

The const keyword before the reference parameter means the function cannot modify the argument. Here, we want to pass by reference, so int &num is correct, and adding const is common to prevent changes.

2fill in blank

medium

Complete the code to call the function swap passing two integers by reference.

C++

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

int main() {
    int x = 5, y = 10;
    swap([1], y);
    return 0;
}

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Ax

B&x

C*x

Dint x

Attempts:

3 left

💡 Hint

Common Mistakes

Using &x in the function call, which is incorrect for references

Using *x which is for pointers

When passing by reference, you just pass the variable name without & or * in the call. The function parameter already expects a reference.

3fill in blank

hard

Fix the error in the function declaration to correctly pass a string by reference.

C++

#include <string>

void printName([1] std::string name) {
    std::cout << name << std::endl;
}

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Aconst std::string &

Bstd::string *

Cstd::string &

Dstd::string

Attempts:

3 left

💡 Hint

Common Mistakes

Passing by value causes unnecessary copying

Using pointer syntax when reference is preferred

Passing a string by const std::string & is efficient and prevents modification. It avoids copying the string.

4fill in blank

hard

Fill both blanks to create a function that doubles an integer passed by reference and call it correctly.

C++

void doubleValue([1] int &num) {
    num *= 2;
}

int main() {
    int val = 7;
    doubleValue([2]);
    return 0;
}

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Aint

Bval

Cconst

D&val

Attempts:

3 left

💡 Hint

Common Mistakes

Using &val in the call which is incorrect for references

Adding const incorrectly in the parameter

The function parameter should be int &num to pass by reference. When calling, just pass the variable val without &.

5fill in blank

hard

Fill all three blanks to create a function that swaps two integers by reference and call it correctly.

C++

void swap([1] int &a, [2] int &b) {
    int temp = a;
    a = b;
    b = temp;
}

int main() {
    int x = 3, y = 4;
    swap([3], y);
    return 0;
}

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

Aint

Bconst

Cx

D&x

Attempts:

3 left

💡 Hint

Common Mistakes

Using const in parameters which prevents modification

Passing &x in the function call which is incorrect

The function parameters should be int &a and int &b to pass by reference. When calling, just pass the variable x without &.