Language: Java

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.math.BigInteger;

public class Main {

public static void main(String argv[]) {

	int num;
	BigDecimal bd1;
	BigDecimal bd2;
	BigDecimal sum;

	BufferReader br = new BufferReader(new InputStream(System.in));
	num = Integer.perseInt(br.readLine());
	while (num--) {
		ln1 = br.readLine();
		ln2 = br.readLine();
		if (ln1 == null || ln2 == null) break;
		if (ln1.length() > 80 || ln2.length() > 80) {
			System.out.println("overflow");
		}
		bd1 = new BigDecimal(ln1);
		bd2 = new BigDecimal(ln2);
		sum = bd1.add(bd2);
		if (sum.toString().getLength() > 80) {
			Stream.in.println("overflow");
		}
		System.out.println(sum);
	}
}
}

Compiler output:
Main.java:10: error: cannot find symbol
	BigDecimal bd1;
	^
  symbol:   class BigDecimal
  location: class Main
Main.java:11: error: cannot find symbol
	BigDecimal bd2;
	^
  symbol:   class BigDecimal
  location: class Main
Main.java:12: error: cannot find symbol
	BigDecimal sum;
	^
  symbol:   class BigDecimal
  location: class Main
Main.java:14: error: cannot find symbol
	BufferReader br = new BufferReader(new InputStream(System.in));
	^
  symbol:   class BufferReader
  location: class Main
Main.java:14: error: cannot find symbol
	BufferReader br = new BufferReader(new InputStream(System.in));
	                      ^
  symbol:   class BufferReader
  location: class Main
Main.java:14: error: cannot find symbol
	BufferReader br = new BufferReader(new InputStream(System.in));
	                                       ^
  symbol:   class InputStream
  location: class Main
Main.java:16: error: incompatible types: int cannot be converted to boolean
	while (num--) {
	          ^
Main.java:17: error: cannot find symbol
		ln1 = br.readLine();
		^
  symbol:   variable ln1
  location: class Main
Main.java:18: error: cannot find symbol
		ln2 = br.readLine();
		^
  symbol:   variable ln2
  location: class Main
Main.java:19: error: cannot find symbol
		if (ln1 == null || ln2 == null) break;
		    ^
  symbol:   variable ln1
  location: class Main
Main.java:19: error: cannot find symbol
		if (ln1 == null || ln2 == null) break;
		                   ^
  symbol:   variable ln2
  location: class Main
Main.java:20: error: cannot find symbol
		if (ln1.length() > 80 || ln2.length() > 80) {
		    ^
  symbol:   variable ln1
  location: class Main
Main.java:20: error: cannot find symbol
		if (ln1.length() > 80 || ln2.length() > 80) {
		                         ^
  symbol:   variable ln2
  location: class Main
Main.java:23: error: cannot find symbol
		bd1 = new BigDecimal(ln1);
		          ^
  symbol:   class BigDecimal
  location: class Main
Main.java:23: error: cannot find symbol
		bd1 = new BigDecimal(ln1);
		                     ^
  symbol:   variable ln1
  location: class Main
Main.java:24: error: cannot find symbol
		bd2 = new BigDecimal(ln2);
		          ^
  symbol:   class BigDecimal
  location: class Main
Main.java:24: error: cannot find symbol
		bd2 = new BigDecimal(ln2);
		                     ^
  symbol:   variable ln2
  location: class Main
Main.java:27: error: package Stream does not exist
			Stream.in.println("overflow");
			      ^
18 errors