如何在循环内外使用来自user的输入变量

Question

char answer = input.next().charAt(0);
for (int i =1 ;i!=0 ; ) {


int j = 0 ; 
if ( answer=='*' ||  answer=='/' || answer=='+' || answer=='-') {
i= 0 ; 
}
else 
{
i=1; 

while ( j<i) {
System.out.println( " please reenter the operation ") ; 
//answer=input.next().charAt(0) ; 
j++ ; 
}

}

}

在这段代码中，我在循环外声明了变量answer来运行代码但是在我的主代码中，我试图将变量放入循环中比如这里的

for (int i =1 ;i!=0 ; ) {
char answer = input.next().charAt(0)  ; 
}

.......

所以循环外的变量不能被使用

Answer 1

我会遵循这样的模式:

char answer;
boolean invalid;    
do {
System.out.print("Operation: ");
answer = input.nextLine().charAt(0);
invalid = (answer != '*' && answer != '/' && answer != '+' && answer != '-');
if (invalid) {
System.out.println("Invalid operation. Please re-enter!");
}
} while (invalid);
// ... do something with "answer" here ...