HOW TO SOLVE THIS IN DART?

Question

import "dart:math";
import "dart:io";

void main(){
  print("enter first number");
  double num1 = double.parse(stdin.readLineSync());
  print("enter second number");
  double num2 = double.parse((stdin.readLineSync());

  print (
    num1 + num2
        );
  
}

Why it doesnt compile

Enter two numbers from the user add them and the program returns their sum.

tell us what is the issue exactly? What error messages you are getting? — Ibrahim shamma, Nov 08 '22 at 08:49

score 1 · Answer 1 · answered Nov 08 '22 at 09:00

For double.parse it needs a String. But stdin.readLineSync() provides nullable String, means this method can return null or string. It is safe to use .tryParse and provide default String instead of using !.

double num1 = double.tryParse(stdin.readLineSync() ?? "") ?? 0;
print("enter second number");
double num2 = double.tryParse((stdin.readLineSync() ?? "")) ?? 0;

print(num1 + num2);

More about tryParse and understanding-null-safety

score 0 · Answer 2 · answered Nov 08 '22 at 08:59

There are 2 issues. First, double.parse requires a String, but readLineSync returns a String?. To solve, simply convert it by using the ! operator, like

 double num1 = double.parse(stdin.readLineSync()!);

The second issue is that you have a ( too many at the num2 = double.parse(( part, so change

double num2 = double.parse((stdin.readLineSync());

to

double num2 = double.parse(stdin.readLineSync()!);

HOW TO SOLVE THIS IN DART?

2 Answers2