The operator '>' isn't defined for the type 'String'. Try defining the o-CodePudding

i wrote this code :

void main() {
  int kian = 40;
  if (kian > 10) {
    print('mamad');
  }
}

and now for run I have this error : The operator '>' isn't defined for the type 'String'. Try defining the operator '>'.

how can i fix it? i will be so happy if you answer me :)

CodePudding user response：

You were trying to compare two variables which were of type String.

void main() {
  String kian = '40';
  if (kian > '10') {
    print('mamad');
  }
}

//Error message:  line 3 • The operator '>'
// isn't defined for the type 'String'.
//Try defining the operator '>'.

However, in your question you provided a running code. Check it here.

CodePudding user response：

With the code, it working fine cause it type is int. The error may throw from another place.

In case your variable is String of number like this String kian = '40'; you can write your custom operator in a extension to able to compare them but not recommend. Except you are 100% sure it is an number.

void main() {
  try{
    print("'40' > '10': ${'40' > '10'}");
    print("'40' < '10': ${'40' < '10'}");
    
    print("'40' >= '10': ${'40' >= '10'}");
    print("'40' <= '10': ${'40' <= '10'}");
  }catch(e){
    print('error. the string is not a number');
  }
}

extension on String {
  operator >(String other){
    return double.parse(this) > double.parse(other);
  }
  operator >=(String other){
    return double.parse(this) >= double.parse(other);
  }
  operator <(String other){
    return double.parse(this) < double.parse(other);
  }
  operator <=(String other){
    return double.parse(this) <= double.parse(other);
  }
}

Result

'40' > '10': true
'40' < '10': false
'40' >= '10': true
'40' <= '10': false