嵌套循环表示另一个循环语句中的循环语句。这就是为什么嵌套循环也称为“循环内循环”的原因。
嵌套For循环的语法：
for ( initialization; condition; increment ) {
for ( initialization; condition; increment ) {
// statement of inside loop
}
// statement of outer loop
}
嵌套While循环的语法：
while(condition) {
while(condition) {
// statement of inside loop
}
// statement of outer loop
}
嵌套Do-While循环的语法：
do{
do{
// statement of inside loop
}while(condition);
// statement of outer loop
}while(condition);
Note: There is no rule that a loop must be nested inside its own type. In fact, there can be any type of loop nested inside any type and to any level.
句法：
do{
while(condition) {
for ( initialization; condition; increment ) {
// statement of inside for loop
}
// statement of inside while loop
}
// statement of outer do-while loop
}while(condition);
下面是一些示例来演示嵌套循环的用法：
示例1：下面的程序使用嵌套的for循环打印3×3的2D矩阵。
// C++ program that uses nested for loop
// to print a 2D matrix
#include
using namespace std;
#define ROW 3
#define COL 3
// Driver program
int main()
{
int i, j;
// Declare the matrix
int matrix[ROW][COL] = { { 1, 2, 3 },
{ 4, 5, 6 },
{ 7, 8, 9 } };
cout << "Given matrix is \n";
// Print the matrix using nested loops
for (i = 0; i < ROW; i++) {
for (j = 0; j < COL; j++)
cout << matrix[i][j];
cout << "\n";
}
return 0;
}
输出：
Given matrix is
123
456
789
示例2：下面的程序使用嵌套的for循环来打印数字的所有素数。
// C++ Program to print all prime factors
// of a number using nested loop
#include
using namespace std;
// A function to print all prime factors of a given number n
void primeFactors(int n)
{
// Print the number of 2s that divide n
while (n % 2 == 0) {
cout << 2;
n = n / 2;
}
// n must be odd at this point. So we can skip
// one element (Note i = i +2)
for (int i = 3; i <= sqrt(n); i = i + 2) {
// While i divides n, print i and divide n
while (n % i == 0) {
cout << i;
n = n / i;
}
}
// This condition is to handle the case when n
// is a prime number greater than 2
if (n > 2)
cout << n;
}
/* Driver program to test above function */
int main()
{
int n = 315;
primeFactors(n);
return 0;
}
输出：
3357
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