[Java] Calculator program

2 minute read

//キーボード入力インポート
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.math.BigDecimal;

//クラス開始
public class Original {

//メインメソッド開始**********
public static void main(String[] args) throws IOException {

//キーボード入力準備
BufferedReader br =
new BufferedReader (new InputStreamReader(System.in));

	String now = "0";
	String input = "";
	String enzan = "";  String msg = "Numeric";
	String data = "";

//無限ループ
while(true){
try {

			//******************************************
			System.out.println("\n"+"***************************");
			System.out.println(" ");  System.out.println ("Current value:" + now);  System.out.println ("operator:" + enzan);  System.out.println ("Entered value:" + input);  Enter System.out.print (msg + ">>");
			//******************************************

//dataに入力値を代入する
data = br.readLine();

			//A-1
			if(hantei(data)){  BigDecimal bd_data = new BigDecimal (data); // Convert to Decimal
				BigDecimal er = new BigDecimal(0);

bd_data = bd_data.stripTrailingZeros (); // Erase zero

				//B-1  if ("numerical value" .equals (msg)) {
					now = bd_data.toPlainString();  msg = "operator";

					//C-1  } else if ("numerical or operator" .equals (msg)) {
					//D-1
					if("/".equals(enzan) && bd_data.equals(er)){  System.out.println ("doesn't break at 0");

					}else{
						input = bd_data.toPlainString();  msg = "operator";
					}
					//C-1
				}else{  System.out.println ("Error! Please enter operator" + "\ n");
				}


				//A-2
			}else{
if(“+”.equals(data) || “-“.equals(data) ||
“*“.equals(data) || “/”.equals(data) ||
						"=".equals(data)){

//msgが数値のとき
if (“numerical value” .equals (msg)) {
System.out.print (“Error! Please enter a number”);

//msgが数値又は演算子のとき
} else if (“numerical or operator” .equals (msg)) {

//dataが=だったら
if(“=”.equals(data)){
System.out.print (“Error! Please enter a number”);
}else{
enzan = data;
msg = “Numeric or operator”;
}

//msgが演算子のとき
}else{

//inputが空だったら
if(““.equals(input)){
if(“=”.equals(data)){
System.out.print (“Error! Please enter something other than equal”);
}else{
enzan = data;
msg = “Numeric or operator”;
}

//inputに値が入っていたら
}else{

							BigDecimal bd1 = new BigDecimal(now);
							BigDecimal bd2 = new BigDecimal(input);

//足し算
if(“+”.equals(enzan)){
BigDecimal ans1 = bd1.add(bd2);

								now = ans1.toPlainString();
								input = "";

//引き算
}else if(“-“.equals(enzan)){
BigDecimal ans2 = bd1.subtract(bd2);

								now = ans2.toPlainString();
								input = "";

//掛け算
}else if(“*“.equals(enzan)){
BigDecimal ans3 = bd1.multiply(bd2);

								now = ans3.toPlainString();
								input = "";

//割り算(四捨五入・20桁まで表示)
}else{
BigDecimal ans4 = bd1.divide(bd2,20,BigDecimal.ROUND_HALF_UP);

								ans4 = ans4.stripTrailingZeros();
								now = ans4.toPlainString();
								input = "";
							}

//dataが=だった場合
if(“=”.equals(data)){
enzan = “”;
//=でない場合
}else{
enzan = data;
msg = “Numeric or operator”;
}
} // If there is a value in input
} // When msg is an operator

					//A-3
				}else if("c".equals(data)){
					now = "0";
					enzan = "";
					input = "";  msg = "numerical value";  System.out.print ("cleared");


					//A-4
				}else if("ce".equals(data)){

					//B-3
					if(input != ""){
						input = "";  msg = "Numeric or operator";
						//C-3
					}else{
						if(enzan != ""){
							enzan = "";  msg = "operator";

						}else{
							now = "0";  msg = "numerical value";
						}
					}

					//A-5
				}else if("e".equals(data)){  System.out.print ("Exit the program");
					break;
				}else{  System.out.print ("\ n" + "error! Unsupported input value");
				}

			}//A-2
		}catch (Exception e) {  // TODO auto-generated catch block  System.out.print ("Unexpected error");
			e.printStackTrace();
		}  }//infinite loop  } // Method

//判定メソッド**************
public static boolean hantei(String data){

	boolean brea = true;

	try{
		Double.parseDouble(data);

	}catch (NumberFormatException e){
		brea = false;
	}
	return	brea;

} //************************************************** }

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