03 Loops

January 5, 2024 · 1 min read

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Use == to compare primitive data types for equality; for other types (such as strings and functions), use equals to compare them.

`while` Loops #

Note: In C++, you can write while(n--), but in Java you must write while(n-- > 0), or the code will not compile.

Find the nth term of the Fibonacci sequence. f(1) = 1, f(2) = 1, f(3) = 2, f(n) = f(n-1) + f(n-2)

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();

        int a = 1, b = 1, i = 1;
        while (i < n) {
            int c = a + b;
            a = b;
            b = c;
            i ++ ;
        }

        System.out.println(a);
    }
}

`do while` Loops #

do while loops are not commonly used.
A do while statement is very similar to a while statement. The only difference is that a do while statement checks the condition after executing the loop body. Regardless of the condition’s value, the loop body executes at least once.

public class Main {
    public static void main(String[] args) {
        int x = 1;
        while (x < 1) {
            System.out.println("x!");
        }

        int y = 1;
        do {
            System.out.println("y!");
        } while (y < 1);
    }
}

`for` Loops #

Find the nth term of the Fibonacci sequence. f(1) = 1, f(2) = 1, f(3) = 2, f(n) = f(n-1) + f(n-2).

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();

        int a = 1, b = 1;
        for (int i = 1; i < n; i ++ ) {
            int c = a + b;
            a = b;
            b = c;
        }

        System.out.println(a);
    }
}

Jump Statements #

break #

Exits a loop early, usually together with an if statement.

continue #

Jumps directly to the end of the current loop iteration.

Find the sum of all even numbers from 1 to 100.

public class Main {
    public static void main(String[] args) {
        int sum = 0;
        for (int i = 1; i <= 100; i ++ ) {
            if (i % 2 == 1) continue;
            sum += i;
        }
        System.out.println(sum);
    }
}

03 Loops

January 5, 2024 · 1 min read

while Loops #

do while Loops #

for Loops #