如何在if陳述句下定義布林值

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


String promptStudent(){
print("are you a student?");
String Student = stdin.readLineSync()!;
return Student;
}

String promptSmart(){
print("2 2=?");
String Smart = stdin.readLineSync()!;
return Smart;
}



void main() {
  String student = promptStudent();
  if(student == "yes"){
  bool isStudent = true;
  } else() {
  bool isStudent = false;
  };
  String smart = promptSmart();
  if(smart == "4"){
  bool isSmart = true;
  } else() {
  bool isSmart = false;
  };

  if(isSmart && isStudent) {
  print("he is a smart student");
  }
  else if(isSmart && !isStudent) {
  print("he is smart but not a student");
  }
  else if(!isSmart && isStudent) {
  print("he isnt smart but a student");
  }
  else if(!isSmart && !isStudent) {
  print("he is not smart and not a student");
  };

}

我想通過用戶輸入設定一個布林值（如果 2 2 的答案是 4 他很聰明等），但我遇到了如下問題：

main.dart:42:24: 錯誤：找不到 Getter：'isStudent'。否則 if(!isSmart && !isStudent) {

這里有什么問題？我該如何解決？

uj5u.com熱心網友回復：

在isStudent和isSmart變數具有塊范圍在您創建的if-else陳述句。它們的范圍僅限于{}包圍它們的大括號。因此，您無法在這些部分之外訪問它們。

要訪問 if-else 塊范圍之外的變數，您需要在它之外宣告變數。在 if-else 塊之外宣告變數并在 if-else 塊內分配它們。下面的代碼還修復了各種其他語法錯誤，包括洗掉else陳述句后面的大括號、if-else 塊后面的分號、洗掉未使用的匯入和修復命名約定。

import "dart:io";

String promptStudent() {
  print("are you a student?");
  String student = stdin.readLineSync()!;
  return student;
}

String promptSmart() {
  print("2 2=?");
  String smart = stdin.readLineSync()!;
  return smart;
}

void main() {
  String student = promptStudent();
  late final bool isStudent;
  if (student == "yes") {
    isStudent = true;
  } else {
    isStudent = false;
  }
  String smart = promptSmart();
  late final bool isSmart;
  if (smart == "4") {
    isSmart = true;
  } else {
    isSmart = false;
  }

  if (isSmart && isStudent) {
    print("he is a smart student");
  } else if (isSmart && !isStudent) {
    print("he is smart but not a student");
  } else if (!isSmart && isStudent) {
    print("he isnt smart but a student");
  } else if (!isSmart && !isStudent) {
    print("he is not smart and not a student");
  }
}

您還可以通過多種方式簡化代碼，尤其是在分配布林值時。

這個

late final bool isStudent;
if (student == "yes") {
  isStudent = true;
} else {
  isStudent = false;
}

可以簡化為這個單行：

final bool isStudent = student == "yes";

這使您的代碼變得更簡單：

import "dart:io";

String promptStudent() {
  print("are you a student?");
  return stdin.readLineSync()!;
}

String promptSmart() {
  print("2 2=?");
  return stdin.readLineSync()!;
}

void main() {
  String student = promptStudent();
  final bool isStudent = student == "yes";
  
  String smart = promptSmart();
  final bool isSmart = smart == "4";

  if (isSmart && isStudent) {
    print("he is a smart student");
  } else if (isSmart && !isStudent) {
    print("he is smart but not a student");
  } else if (!isSmart && isStudent) {
    print("he isnt smart but a student");
  } else if (!isSmart && !isStudent) {
    print("he is not smart and not a student");
  }
}

uj5u.com熱心網友回復：

我相信問題在于您的 isStudent 和 isSmart 的范圍。嘗試這個：

void main() {
  String student = promptStudent();
  bool isStudent = false;
  if(student == "yes"){
    isStudent = true;
  }

  String smart = promptSmart();
  bool isSmart = false;
  if(smart == "4"){
    isSmart = true;
  }
  ...

uj5u.com熱心網友回復：

代碼有一些多余的圖片，可能會導致手頭的錯誤，避免定義一些用于比較的變數的定義，如下重寫應該可以解決它，但我無法測驗自己，因為我的標題沒有共享。

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


String promptStudent(){
print("are you a student?");
String Student = stdin.readLineSync()!;
return Student;
}

String promptSmart(){
print("2 2=?");
String Smart = stdin.readLineSync()!;
return Smart;
}



void main() {
  bool isStudent = false;
  bool isSmart = true;
  String student = promptStudent();
  if(student == "yes"){
     isStudent = true;
  }
  String smart = promptSmart();
  if(smart == "4"){
     isSmart = true;
  } 

  if(isSmart && isStudent) {
  print("he is a smart student");
  }
  else if(isSmart && !isStudent) {
  print("he is smart but not a student");
  }
  else if(!isSmart && isStudent) {
  print("he isnt smart but a student");
  }
  else if(!isSmart && !isStudent) {
  print("he is not smart and not a student");
  };

}

標籤：镖 if 语句 布尔值

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