Easy
Print numbers from 1 to 10 (for loop)
Write a programme that prints numbers from 1 to 10 using a for loop.
Show answer:
for (int i = 1; i <= 10; i++) {
System.out.println(i);
}Print even numbers from 1 to 20
Write a programme that prints all even numbers between 1 and 20 using a for loop.
Show answer:
for (int i = 2; i <= 20; i += 2) {
System.out.println(i);
}
}Sum of first 5 numbers
Write a programme to calculate the sum of the first 5 natural numbers using a while loop.
Show answer:
int sum = 0;
int i = 1;
while (i <= 5) {
sum += i;
i++;
}
System.out.println("Sum: " + sum); // prints 15Print numbers from 1 to 10 (do-while loop)
Write a programme that prints numbers from 1 to 10 using a do-while loop.
Show answer:
int i = 1;
do {
System.out.println(i);
i++;
} while (i <= 10);Medium
Reverse a String (Using a for loop)
Write a programme that prints a string in reverse using a for loop. For example, for the input "Hello", the output should be "olleH".
Show answer:
String str = "Hello";
String reversed = "";
for (int i = str.length() - 1; i >= 0; i--) {
reversed += str.charAt(i);
}
System.out.println("Reversed string: " + reversed); // prints "elloH"Sum of odd numbers from 1 to N (Using a while loop)
Write a programme to calculate the sum of all odd numbers from 1 to N, where N is a number entered by the user.
Show answer:
import java.util.Scanner;
Scanner scanner = new Scanner(System.in);
System.out.print("Enter a number: ");
int n = scanner.nextInt();
int sum = 0;
int i = 1;
while (i <= n) {
sum += i;
i += 2; // causes i to skip even numbers, given that i is initialised to number 1;
System.out.println(i);
}
System.out.println("Sum of odd numbers from 1 to " + n + ": " + sum);Find the largest number in an array (Using a while loop)
Write a programme that finds and prints the largest number in the array below using a while loop.
int[] numbers = {10, 23, 45, 32, 89, 50};Show answer:
int[] numbers = {10, 23, 45, 32, 89, 50};
int largest = numbers[0];
int i = 1;
while (i < numbers.length) {
if (numbers[i] > largest) {
largest = numbers[i];
}
i++;
}
System.out.println("Largest number: " + largest);Hard
Print a right-angled triangle pattern (Using a for loop)
Write a programme to print the following right-angled triangle pattern using stars (*):
*
**
***
****
*****Show answer:
for (int i = 1; i <= 5; i++) {
for (int j = 1; j <= i; j++) {
System.out.print("*");
}
System.out.println();
}Print a diamond pattern (Using nested for loops)
Write a programme that prints the following diamond pattern using stars (*):
*
***
*****
*******
*********
*******
*****
***
*
Show answer:
int n = 5; // Number of rows in the top half of the diamond
// Upper part
for (int i = 1; i <= n; i++) {
for (int j = i; j < n; j++) {
System.out.print(" ");
}
for (int k = 1; k <= (2 * i - 1); k++) {
System.out.print("*");
}
System.out.println();
}
// Lower part
for (int i = n - 1; i >= 1; i--) {
for (int j = n; j > i; j--) {
System.out.print(" ");
}
for (int k = 1; k <= (2 * i - 1); k++) {
System.out.print("*");
}
System.out.println();
}
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