英文:
Can we use semicolon independently at the beginning of a for-loop?
问题
public class ReverseNumber {
public static void main(String[] args) {
int num = 1234567, reversed = 0;
for (; num != 0; num /= 10) { // <-- meaning of the first ; ?
int digit = num % 10;
reversed = reversed * 10 + digit;
}
System.out.println("Reversed Number: " + reversed);
}
}
这个for循环中第一个分号之前的部分是循环的初始化部分，第二个分号之前的部分是循环的条件部分，决定是否继续循环，第二个分号之后的部分是循环的迭代部分，用于更新循环控制变量。
英文:
What is the meaning of this type of syntax in the for-loop?
public class ReverseNumber {
public static void main(String[] args) {
int num = 1234567, reversed = 0;
for (; num != 0; num /= 10) { // <-- meaning of the first ; ?
int digit = num % 10;
reversed = reversed * 10 + digit;
}
System.out.println("Reversed Number: " + reversed);
}
}
答案1
得分: 2
一个 for 语句由三个部分组成 for（语句A; 语句B; 语句C）：
- 语句A 是初始化语句。它只执行一次。通常情况下，您在for循环中创建要使用的变量。
- 语句B 是停止条件。它在每次开始for循环时执行，用于确定是否应该再次执行for循环。
- 语句C 是在每次for循环结束时执行的操作（比如递增您的变量）。
它们都是可选的。
以下是一些for循环的示例：
for (;;) {
// 无限循环
}
for (int i = 0; i < 10; i++) {
// 循环10次，并在每次循环时递增i
}
int b = i; // 不可能的，i不再存在
// 这个for循环等同于：
int i = 0;
for (; i < 10; i++) {
// 几乎相同。不同之处在于在for循环之后可以访问i
}
int b = i; // 可以，因为i仍然可见。
for (int a = 0;; a++) {
// 无限循环（因为没有停止条件）来递增变量a
System.out.println(a);
}
for (int constant = 0;;) {
// 无限循环（没有停止条件），您可以使用常量变量（但始终为0）
System.out.println(constant);
}
英文:
A for statement is composed of 3 parts for(statement A; statement B; statement C):
- Statement A is the initializer statement. It is executed only one time. Usually, you create your variables you want to use in the for loop
- Statement B is the stop condition. It is executed every time at the beginning of the for loop, to determine if you should do the for loop one more time
- Statement C is the operation to execute every time at the end of the for loop (like incrementing your variable for instance).
All of them are optional.
Here some examples of for loop:
for(;;) {
// infinite loop
}
for(int i = 0; i < 10; i++) {
// Loop 10 times and increment i each time
}
int b = i; // impossible. i does not exist anymore
// this for is equivalent to :
int i = 0;
for(; i < 10; i++) {
// Almost the same. The difference here is that I can be accessed after the for loop
}
int b = i; // possible, because i is still visible.
for(int a = 0;; a++) {
// Infinite loop (because no stop condition) to increment variable a
System.out.println(a);
}
for(int constant = 0;;) {
// Infinite loop (no stop condition) and you can use constant variable (but will always be 0)
System.out.println(constant);
}
答案2
得分: 0
如果您在循环开始时使用分号;，这意味着您尚未初始化其值。
在下面的示例中：
int num = 1234567, reversed = 0;
for(;num != 0; num /= 10) {
int digit = num % 10;
reversed = reversed * 10 + digit;
}
它已经在获取变量“num”的值。
如果您注释掉“num”的赋值，您将会得到一个错误。
英文:
if you are using ; in the beginning of the loop that means , you don't have already initialized its value
in the below exapmle:
int num = 1234567, reversed = 0;
for(;num != 0; num /= 10) {
int digit = num % 10;
reversed = reversed * 10 + digit;
}
it is already picking the value of "num"
In case if you comment the num value you will get an error.
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