I'm trying to sum of the number in a String but can't filter in if() condition

    String name = 'saran7711@7';
    int length = name.length;
    int store = 0;
    for (int i = 0; i < length; i++) {
      int? nameInt = int.tryParse(name[i]);
      if (nameInt == null) continue;
      // if the name us a string then skip it and move to next letter
      store = store + nameInt;
    }
    print(store);

You cannot compare directly compare the element at index name[i] as this evaluates to a string and not a numerical value, your approach is trying to compare individual characters of a string (name[i]) using relational operators (>= and = 0 && name[i].compareTo('9')

You are treating name[i] as if it was a number, when it's a string.

Instead use codeUnitAt to extract the number:

  const c0 = 0x30, c9 = 0x39; // Code units for 0 and 9 digits.
  String name = 'saran7711@7';
  int store = 0;
  for (int i = 0; i < name.length; i++) {
    var char = name.codeUnitAt(i);
    if (char >= c0 && char 

You can test this code in dartpad:

void main() {
  String name = 'saran7711@7';
  print(name); // saran7711@7
  int length = name.length;
  int store = 0;
  for (int i = 0; i < length; i++) {
    if (RegExp(r'[0-9]').hasMatch(name[i])) {
      store += int.parse(name[i]);
    }
  }
  print(store); // 23
}

You can also use RegExp class with hasMatch abstract method to filter out a certain characters you want to extract (i.e., raw string from 0 to 9), and also by incorporating int parsing of the extracted numeric data before performing addition on it. The += (addition assignment operator) will work well for this, as it allows you to accumulate each new numeric value from name[i] with every iteration, until all available data has been processed.