C program to print 1 to n natural numbers

Understanding the Problem

• Goal: Write a C program that takes a positive integer n from the user and prints all natural numbers from 1 to n.
• Key Concepts:
  • Variables: Containers for storing data (n).
  • Loops: Used to repeat code blocks (for loop in this case).
  • Input/Output (I/O): Communicating with the user (scanf, printf).

Step-by-Step Guide

1. Header Inclusion

C

#include <stdio.h>

This line includes the standard input/output library, providing functions for printing to the console (e.g., printf) and reading user input (e.g., scanf).

2. Variable Declaration

C

int n;

This declares an integer variable named n to store the user-provided positive integer.

3. Get User Input

C

printf("Enter a positive integer: ");

// Loop for input validation
do {
    // Scan for integer input
    if (scanf("%d", &n) != 1) {
        printf("Invalid input. Please enter a positive integer: ");
        // Clear input buffer to avoid infinite loop
        scanf("%*c");
    }
} while (n <= 0);

• printf: Prompts the user to enter a positive integer.
• do-while loop: Ensures valid input.
• scanf("%d", &n): Reads the user’s input and stores it in the n variable.
• if (scanf("%d", &n) != 1): Checks if the scan was successful and if only one integer was entered.
• printf("Invalid input..."): Informs the user of invalid input and loops again.
• scanf("%*c"): Clears the input buffer from any leftover characters to avoid misreading in the next iteration.

4. Printing Numbers

C

// For loop to iterate from 1 to n
for (int i = 1; i <= n; i++) {
    printf("%d\n", i);
}

• for loop:
  • Initializes i to 1.
  • Checks if i is less than or equal to n.
  • Increments i by 1 each iteration.
• printf("%d\n", i): Prints the current value of i (the loop counter) followed by a newline.

5. Complete Code

C

#include <stdio.h>

int main() {
    int n;

    printf("Enter a positive integer: ");

    do {
        if (scanf("%d", &n) != 1) {
            printf("Invalid input. Please enter a positive integer: ");
            scanf("%*c");
        }
    } while (n <= 0);

    for (int i = 1; i <= n; i++) {
        printf("%d\n", i);
    }

    return 0;
}

6. Executing the Program

1. Save the code as a .c file (e.g., print_naturals.c).
2. Open a terminal or command prompt.
3. Navigate to the directory where you saved the file.
4. Compile the code using a C compiler (e.g., gcc print_naturals.c -o print_naturals).
5. Run the compiled executable (e.g., ./print_naturals).

7. Example Output

Enter a positive integer: 5 1 2 3 4 5

This program is now complete and should function as intended.