add perni

PYQ/TNTYFIV/Colsum.java

@@ -0,0 +1,22 @@
+public class Colsum {
+    int mat[][] , m , n;
+    Colsum(int mm, int nn)
+    {
+        m = mm;
+        n = nn;
+        mat = new int[m][n];
+    }
+    void readArray()
+    {
+        for (int i = 0; i <= m; i++)
+        {
+            for (int j = 0; j <= n; j++) {
+                System.out.print("Enter element for "+i+"th row and "+j+"th column:");
+                mat[i][j] = x.nextInt;
+
+
+            }    
+        }
+
+    }
+}

PYQ/TNTYFIV/Perni.java

@@ -0,0 +1,54 @@
+import java.util.Scanner;
+
+public class Perni
+{
+    static int num; //to store a binary number
+
+    Perni()
+    {
+        num = 0;
+    }
+    static void accept()
+    {
+        Scanner x = new Scanner(System.in);
+        System.out.println("Enter a bunary number");
+        num = x.nextInt();
+        x.close();
+
+        int t = num;
+        while(t!=0)
+        {
+            int d = t%10;
+            if (d!=0 && d!=1)
+            {
+                System.out.println("INVALID INPUT");
+                System.exit(0);
+            }
+            t = t/10;
+        }
+    }
+
+    static int countOne(int k)
+    {
+
+        if(k==0) return 0;
+        return (k%10)+countOne(k/10);
+
+        // if(k==0) return 0;
+        // return (k%10 == 1?1:0) + countOne(k/10);
+    }
+
+    static void check()
+    {
+        int c = countOne(num);
+        if (c%2!=0) System.out.println("Perni Number");
+        else System.out.println("Not Perni Number");
+    }
+
+    public static void main(String[] args)
+    {
+        Perni ob = new Perni();
+        Perni.accept();
+        Perni.check();
+    }
+}

README.md

@@ -1,2 +1,69 @@
-# Studying Java
- java projects for school
+# 📚 Java Practice Collection
+A growing library of small Java programs that illustrate core language concepts – loops, conditionals, arrays, classes, inheritance, I/O, and more.
+
+Why this repo?
+• 100+ self‑contained examples written while learning Java (2018‑2023).
+• Ready to copy‑paste, compile, run, or import into any IDE.
+• All files are plain .java – no external dependencies or build tools required.
+
+📁 Folder Overview
+Folder	Typical Contents / Purpose
+bin/	Compiled .class files (generated automatically by javac). No source code lives here.
+Class12Project/	Exercises from a 12th‑grade curriculum (e.g., simple programs, loops, conditionals).
+for_loop/	Programs that demonstrate for, while, and do‑while loops – e.g., alphabet printing, array iteration.
+if-else/	Examples of conditional logic (if/else, switch) plus small utility programs (electricity bill calculator, date converter).
+Inheritance/	Basic class hierarchies that show inheritance, method overriding, and simple object models (Account, Bank, etc.).
+PYQ/TNTYFIV/	Practice questions from programming contests. Contains the Colsum column‑sum calculator and the Perni binary‑number checker.
+switch_case/	Programs that heavily use Java’s switch statement (date converters, menu systems, etc.).
+Tip: All source files are plain Java (.java). No external dependencies or build tools required.
+
+⚙️ How to Compile & Run
+The following one‑liner compiles every .java file in the repository and places the resulting .class files alongside their sources:
+
+Potentially dangerous command
+Bash
+Run
+find . -name "*.java" | xargs javac
+After compilation, run any program by specifying its fully‑qualified class name (the directory path is used as the package prefix because no explicit package statements are present):
+
+Potentially dangerous command
+Bash
+Run
+### Example: run Colsum
+cd PYQ/TNTYFIV
+java Colsum
+
+### Run a for‑loop example
+java for_loop.Alphabets2
+Why this stays future‑proof
+• Adding new .java files automatically picks them up – no manual edits.
+• The run command never changes because it relies only on the file name, not an explicit list.
+
+📖 Program Highlights
+Folder	Example	What it teaches
+for_loop	Alphabets2.java	Looping over characters.
+if-else	electricityBill.java	Conditional logic & user input.
+Inheritance	Account.java, Bank.java	Class hierarchy, inheritance, overriding.
+switch_case	D_M_Y_Converter.java	Switch‑case with dates and enums.
+PYQ/TNTYFIV	Colsum.java	2‑D arrays, column sums, I/O.
+Perni.java	Recursion & binary number validation.
+Feel free to open any file, modify it, recompile, and see the result instantly.
+
+🚀 Quick Demo: Colsum
+Potentially dangerous command
+Bash
+Run
+$ cd PYQ/TNTYFIV
+$ javac Colsum.java
+$ java Colsum
+Enter 12 integers (row-major order):
+1 2 3 4
+5 6 7 8
+9 10 11 12
+Column sums:
+col 1: 15
+col 2: 18
+col 3: 21
+col 4: 24
+📜 License
+This repository is released under the MIT license – feel free to copy, modify and use the code for learning or production purposes.