是否可以使用break函数退出几个嵌套的for循环?
如果是,你会怎么做呢?你还能控制刹车出多少圈吗?
是否可以使用break函数退出几个嵌套的for循环?
如果是,你会怎么做呢?你还能控制刹车出多少圈吗?
当前回答
虽然这个答案已经提出了,但我认为一个很好的方法是这样做:
for(unsigned int z = 0; z < z_max; z++)
{
bool gotoMainLoop = false;
for(unsigned int y = 0; y < y_max && !gotoMainLoop; y++)
{
for(unsigned int x = 0; x < x_max && !gotoMainLoop; x++)
{
//do your stuff
if(condition)
gotoMainLoop = true;
}
}
}
其他回答
Breaking out of a for-loop is a little strange to me, since the semantics of a for-loop typically indicate that it will execute a specified number of times. However, it's not bad in all cases; if you're searching for something in a collection and want to break after you find it, it's useful. Breaking out of nested loops, however, isn't possible in C++; it is in other languages through the use of a labeled break. You can use a label and a goto, but that might give you heartburn at night..? Seems like the best option though.
不,别打断我的表演。这是使用后藤的最后一个据点。
我的建议是使用一个检查变量来打破一个期望的循环。结果代码可能不那么令人愉快。 您可以使用预处理器,以便在引擎盖下进行所需的破坏。这种方法可以隐藏丑陋的代码和额外的复杂性。 例如,我创建了自定义中断机制,如下所示:
想要的代码:
for (int i = 0; i < 100; i++) {
for (int j = 0; j < 100; j++) {
for (int k = 0; k < 100; k++) {
//do something
if (desiredCondition) {
breakToLevel = 0;
}
if (breakToLevel < 3) {
break;
}
}
if (breakToLevel < 2) {
break;
}
}
if (breakToLevel < 1) {
break;
}
}
宏定义:
#define BREAK_TO(L) breakToLevel = (L);
#define CHECK_BREAK(L) if (breakToLevel < (L)) break;
和结果:
for (int i = 0; i < 100; i++) {
for (int j = 0; j < 100; j++) {
for (int k = 0; k < 100; k++) {
//do something
if (desiredCondition) {
BREAK_TO(0)
}
CHECK_BREAK(3)
}
CHECK_BREAK(2)
}
CHECK_BREAK(1)
}
你可以使用“goto”来留下嵌套循环 下面是我的原始代码,包括“goto”
int main()
{
string str;
while (cin >> str)
{
if (str == "0")
break;
int sum = 0;
for (auto ch : str)
{
if (ch <= 'z' && ch >= 'a')
sum += (ch - 'a' + 1);
else if (ch >= 'A' && ch <= 'Z')
sum += (ch - 'A' + 1);
else
{
cout << "Fail" << endl;
goto fail;
}
}
cout << sum << endl;
fail:
}
return 0;
}
然而,我可以通过添加函数“计算”来避免“goto”
void calculate(const string &str)
{
int sum = 0;
for (auto ch : str)
{
if (ch <= 'z' && ch >= 'a')
sum += (ch - 'a' + 1);
else if (ch >= 'A' && ch <= 'Z')
sum += (ch - 'A' + 1);
else
{
cout << "Fail" << endl;
return;
}
}
cout << sum << endl;
}
int main()
{
string str;
while (cin >> str)
{
if (str == "0")
break;
calculate(str);
}
return 0;
}
打破几个嵌套循环的一个好方法是将代码重构为一个函数:
void foo()
{
for(unsigned int i=0; i < 50; i++)
{
for(unsigned int j=0; j < 50; j++)
{
for(unsigned int k=0; k < 50; k++)
{
// If condition is true
return;
}
}
}
}