# Java Program to Display Numbers and Sum of First N Natural Numbers

Print first N natural numbers using an iterative approach i.e. using for loop. For loop has three parameters initialization, testing condition, and increment/decrement.

Input: N = 10 Output: First 10 Numbers = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 Sum of first 10 Natural Number = 55 Input: N = 5 Output: First 5 Numbers = 1, 2, 3, 4, 5 Sum of first 5 Natural Number = 15

**Approach**

- Start for loop initialization with i = 1.
- Write testing condition as i <= N.
- Add increment statement as i++ or i+=1.
- Initialize a variable sum with 0.
- Start adding i with the sum at each iteration of for loop and print i.
- Print sum at the end for loop.

Below is the implementation of above approach

## Java

`// Java Program to Display Numbers` `// from 1 to N Using For Loop and` `// sum of First N Natural Number` `import` `java.io.*;` `class` `GFG {` ` ` `public` `static` `void` `main(String[] args)` ` ` `{` ` ` `int` `N = ` `10` `;` ` ` `int` `sum = ` `0` `;` ` ` `System.out.print(` `"First "` `+ N + ` `" Numbers = "` `);` ` ` ` ` `// we initialize the value of the variable i ` ` ` `// with 1 and increment each time with 1` ` ` `for` `(` `int` `i = ` `1` `; i <= N; i++) {` ` ` ` ` `// print the value of the variable as` ` ` `// long as the code executes` ` ` `System.out.print(i + ` `" "` `);` ` ` `sum += i;` ` ` `}` ` ` `System.out.println();` ` ` `System.out.println(` `"Sum of first "` `+ N` ` ` `+ ` `" Natural Number = "` `+ sum);` ` ` `}` `}` |

**Output**

First 10 Numbers = 1 2 3 4 5 6 7 8 9 10 Sum of first 10 Natural Number = 55

**Time Complexity: **O(n)

**Alternate Approach**

- Start for loop initialization with i = 1.
- Write testing condition as i <= N.
- Add increment statement as i++ or i+=1.
- Start Printing i for each iteration.
- Print sum using first N natural number formula at the end of for loop.

Below is the implementation of the above approach

## Java

`// Java Program to Display Numbers` `// from 1 to N Using For Loop and` `// sum of First N Natural Number` `import` `java.io.*;` ` ` `class` `GFG {` ` ` ` ` `public` `static` `void` `main(String[] args)` ` ` `{` ` ` `int` `N = ` `5` `;` ` ` `System.out.print(` `"First "` `+ N + ` `" Numbers = "` `);` ` ` ` ` `// we initialize the value of the variable i` ` ` `// with 1 and increment each time with 1` ` ` `for` `(` `int` `i = ` `1` `; i <= N; i++) {` ` ` ` ` `// print the value of the variable as` ` ` `// long as the code executes` ` ` `System.out.print(i + ` `" "` `);` ` ` `}` ` ` `System.out.println();` ` ` `System.out.println(` `"Sum of first "` `+ N` ` ` `+ ` `" Natural Number = "` `+ (N*(N+` `1` `))/` `2` `);` ` ` `}` `}` |

**Output**

First 5 Numbers = 1 2 3 4 5 Sum of first 5 Natural Number = 15

**Time Complexity: **O(n)

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