C Program for n-th even number

Given a number N we have to find the N-th even number.

Even numbers are the numbers which are completely divided by 2 and their remainder is zero. Like 2, 4, 6, 8, 10, and so on.

If we closely observe the list of even numbers we can also represent them as −

2*1=2, 2*2=4, 2*3=6, 2*4=8, ?.2*N.

So, to solve the problem we can simply multiply the number N with 2, so the result will be the number which is divisible by 2, i.e. the even number.

Syntax

nth_even_number = n * 2;

Example

Input: n = 4
Output: 8
The first 4 even numbers will be 2, 4, 6, 8, ..

Input: n = 10
Output: 20

Algorithm

START
   STEP 1-> DECLARE AND SET n AS 10
   STEP 2-> PRINT n*2 NUMBER
STOP

Example: Finding nth Even Number

#include <stdio.h>

int main() {
    int n = 10;
    int nthEven = n * 2;
    printf("The %d-th even number is: %d<br>", n, nthEven);
    return 0;
}

The 10-th even number is: 20

Example: Interactive Program

Here's a program that calculates the nth even number for different values −

#include <stdio.h>

int main() {
    int numbers[] = {1, 4, 7, 15, 25};
    int size = 5;
    
    printf("n\tn-th Even Number<br>");
    printf("--\t----------------<br>");
    
    for (int i = 0; i < size; i++) {
        int n = numbers[i];
        int nthEven = n * 2;
        printf("%d\t%d<br>", n, nthEven);
    }
    
    return 0;
}

n	n-th Even Number
--	----------------
1	2
4	8
7	14
15	30
25	50

Key Points

• The nth even number is always 2 * n.
• Time complexity is O(1) as we only perform one multiplication.
• Space complexity is O(1) as we use constant extra space.

Conclusion

Finding the nth even number in C is straightforward using the formula 2*n. This mathematical approach provides an efficient solution with constant time complexity.