C++ Program to Convert Kilometers to Miles

You can convert kilometers to miles in C++ by multiplying the kilometers value by 0.621371. For example, use miles = kilometers * 0.621371; to get the miles equivalent.

Examples

Input0

Output0 kilometers is 0 miles

Input5

Output5 kilometers is 3.10686 miles

Input100

Output100 kilometers is 62.1371 miles

How to Think About It

To convert kilometers to miles, understand that 1 kilometer equals approximately 0.621371 miles. So, multiply the input kilometers by 0.621371 to get miles. Then display the result.

Algorithm

1

Get the distance in kilometers from the user

2

Multiply the kilometers by 0.621371 to convert to miles

3

Display the miles value to the user

Code

cpp

#include <iostream>
using namespace std;

int main() {
    double kilometers, miles;
    cout << "Enter distance in kilometers: ";
    cin >> kilometers;
    miles = kilometers * 0.621371;
    cout << kilometers << " kilometers is " << miles << " miles" << endl;
    return 0;
}

Output

Enter distance in kilometers: 5
5 kilometers is 3.10686 miles

Dry Run

Let's trace the input 5 kilometers through the code

1

Input kilometers

User enters 5, so kilometers = 5

2

Calculate miles

miles = 5 * 0.621371 = 3.106855

3

Output result

Prints '5 kilometers is 3.10686 miles'

kilometers	miles
5	3.106855

Why This Works

Step 1: Conversion factor

We use 0.621371 because 1 kilometer equals approximately 0.621371 miles.

Step 2: Multiplication

Multiplying kilometers by the conversion factor gives the equivalent miles.

Step 3: Display output

The program prints the original kilometers and the converted miles for clarity.

Alternative Approaches

Using a function

cpp

#include <iostream>
using namespace std;

double kmToMiles(double km) {
    return km * 0.621371;
}

int main() {
    double km;
    cout << "Enter kilometers: ";
    cin >> km;
    cout << km << " kilometers is " << kmToMiles(km) << " miles" << endl;
    return 0;
}

This approach separates conversion logic into a function for reuse and clarity.

Using constant variable

cpp

#include <iostream>
using namespace std;

int main() {
    const double KM_TO_MILES = 0.621371;
    double km, miles;
    cout << "Enter km: ";
    cin >> km;
    miles = km * KM_TO_MILES;
    cout << km << " km = " << miles << " miles" << endl;
    return 0;
}

Using a constant improves readability and makes it easy to update the conversion factor.

Complexity: O(1) time, O(1) space

Time Complexity

The program performs a single multiplication and input/output operations, so it runs in constant time.

Space Complexity

Only a few variables are used, so the space used is constant.

Which Approach is Fastest?

All approaches run in constant time; using a function or constant variable mainly improves code clarity, not speed.

Approach	Time	Space	Best For
Direct multiplication	O(1)	O(1)	Simple quick conversion
Function	O(1)	O(1)	Reusable code and clarity
Constant variable	O(1)	O(1)	Readability and easy updates