A value of type 'num' can't be assigned to a variable of type 'int'

Question

I am getting error : "A value of type 'num' can't be assigned to a variable of type 'int'." while executing this code. I got the fix. Just wanted to know why this error. Also Do we need to add "!" for every variable operation?

void main() {  
  Map <int, int> val = {1:10};
  int k = val[1]+5;
  //int k = val[1]!+5; //fix
}

o/p dart pad:

Error compiling to JavaScript:
Info: Compiling with sound null safety
Warning: Interpreting this as package URI, 'package:dartpad_sample/main.dart'.
lib/main.dart:3:17:
Error: Operator '+' cannot be called on 'int?' because it is potentially null.
  int k = val[1]+5;
                ^
lib/main.dart:3:17:
Error: A value of type 'num' can't be assigned to a variable of type 'int'.
  int k = val[1]+5;
                ^
Error: Compilation failed.

Answer 1

Just put a not null operator (!) in line 3 as shown

void main() {  
  Map <int, int> val = {1:10};
  int k = val[1]!+5;
  print(k);
}

no issue was raised during execution, please lmk if the issue is still faced.