while(loop-condition) {
    //loop body    
}

int sum = 0, i = 1;

//循环4次，第5次时，i = 5，i < 5为false
while (i < 5) {
    sum += i;
    i++;
}

cout << "5以内的数之和为：" << sum << endl;
//结果为：5以内的数之和为：10

char loop = 'Y';
while (loop == 'Y') {
    //loop body
    cout << "执行" << endl;
    cout << "Do you want to continue? Yes(y or Y) or No(n or N): ";
    cin >> loop;
    //toupper()函数再<cctype>头文件中，把单个字符转换为大写
    loop = toupper(loop);
}

do {
    //loop body
} while (loop-condition);

int sum = 0, i = 1;

//循环4次，第5次时，i = 5，i < 5为false
do {
    sum += i;
    i++;
}while (i < 5);

cout << "5以内的数之和为：" << sum << endl;
//结果为：5以内的数之和为：10

for (initial-action; loop-condition; action-after-each-iteration) {
    //loop body
}

int sum = 0;

//循环4次，第5次时，i = 5，i < 5为false
for (int i = 1; i < 5; i++) {
    sum += i;
}

cout << "5以内的数之和为：" << sum << endl;
//结果为：5以内的数之和为：10

int sum = 0, i = 1;

//此时i的作用域为整个生命周期，而不是for循环
for (; i < 5; i++) {
    sum += i;
}

cout << "5以内的数之和为：" << sum << endl;
//结果为：5以内的数之和为：10

int sum = 0, i = 1;

//循环4次，第5次时，i = 5，i < 5为false
for (; i < 5;) {
    sum += i;
    i++;
}

cout << "5以内的数之和为：" << sum << endl;
//结果为：5以内的数之和为：10

for (int i = 0;i < 10; i++) {
    if (i == 5) {
        //当i=5时，跳出整个循环
        break;
    }
    cout << i << endl;
}

for (int i = 0;i < 10; i++) {
    if (i == 5) {
        //当i=5时，跳过本次循环
        continue;
    }
    cout << i << endl;
}