• Here is a diagram to describe the program without using any algorithms.

» C

(*) Take advantage of using while() loop and getchar() != '\n' to clear buffer input and validate positive integer.

#include <stdio.h>

void clearInputBuffer() {
    int c;
    while ((c = getchar()) != '\n' && c != EOF);
}

int main() {
    int N;
    printf("Enter a positive integer: ");
    scanf("%d", &N);
    
    while (scanf("%d", &N) != 1 || N <= 0) {
        printf("Invalid input. Enter a positive integer: ");
        clearInputBuffer();
    }
    
    printf("Postive Integer: %d", N);
    return 0;
}

» Java

(*) Take advantage of using scanner.hasNextInt() method is used to check if the next token in the input stream is a valid integer before comparing positive or negative numbers.

import java.util.Scanner;

class HelloWorld {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int N;
        
        System.out.print("Enter a positive integer: ");
        
        while(true) {
            if (scanner.hasNextInt()) {
                N = scanner.nextInt();
                if (N > 0) {
                    break;
                }
            }
            System.out.print("Invalid input. Enter a positive integer: ");
            scanner.nextLine(); // Clear the input buffer
        }
        
        System.out.println("Positive Integer: " + N);
        scanner.close();
    }
}

» PHP

<?php
$N;
echo "Enter a positive integer: ";
while(true) {
    $input = trim(fgets(STDIN));
    if (filter_var($input, FILTER_VALIDATE_INT) && $input > 0) {
        $N = intval($input);
        break;
    }
    echo "Invalid input. Please enter a positive integer: ";
}
echo "Positive Integer: $N\n";
?>

» Javascript

let N = 0;
while (true) {
    let input = prompt("Enter a positive integer:");
    
    if (Number.isInteger(Number(input)) && Number(input) > 0) {
        N = parseInt(input);
        break;
    }
    alert("Invalid input. Please enter a positive integer.");
}
console.log("Positive Integer: " + N);

» Python

N = 0

while True:
    try:
        input_value = int(input("Enter a positive integer: "))
        if input_value > 0:
            N = input_value
            break
        else:
            print("Invalid input. Please enter a positive integer.")
    except ValueError:
        print("Invalid input. Please enter a positive integer.")

print("Positive Integer:", N)