[dish of learning notes dog learning C] exercise

1.n The factorial

int main() {
    
	int n = 0;
	int x = 1;
	printf(" Please enter a number ：");
	scanf("%d", &n);
	int i = 0;
	for (i = 1; i <= n; i++) {
    
		x *= i;
	}
	printf("n The factorial is ：%d", x);
	return 0;
}

2. Calculation 1!+2!+3!+……+10!

int main() {
    
	int i = 0, j = 0;
	int ret = 1;
	int sum = 0;
	for (i = 1; i <= 10; i++) {
    
		for (j = 1; j <= i; j++) {
    
			ret *= j;
		}
		sum += ret;
		ret = 1;
	}
	printf("1!+2!+3!+……+10! by ：%d", sum);
	return 0;
}

   Calculation 1!+2!+3!+……+10! Code optimization

int main() {
    
	int i = 0, j = 0;
	int ret = 1;
	int sum = 0;
	for (i = 1; i <= 10; i++) {
    
		ret *= i;
		sum += ret;
	}
	printf("1!+2!+3!+……+10! by ：%d", sum);
	return 0;
}

3. Find a specific number in an ordered array N, To write int binsearch(int x, intv[]); function ： stay v[0]<=v[1]<=v[2]<=……<=v[n-1] Find in the array of X

int main() {
    
	int arr[] = {
     1, 2, 3, 4, 5, 6, 7, 8, 9,10 };
	int k = 7;// The number to find 
	// stay arr Find in this ordered array k（7） Value 
	int sz = sizeof(arr) / sizeof(arr[0]);// The number of elements in the array 

	int left = 0;
	int right = sz - 1;

	while (left <= right) {
    
		int mid = (left + right) / 2;
		if (arr[mid] < k) {
    
			left = mid + 1;
		}
		else if (arr[mid] > k) {
    
			right = mid - 1;
		}
		else {
    
			printf(" eureka , The subscript is ：%d\n", mid);
			break;
		}
	}
	if (left > right) {
    
		printf(" Can't find \n");
	}
	return 0;
}

4. Write code , Delay multiple characters to move from both ends , Converging in the middle

int main() {
    
	char arr1[] = {
     "I want to reason with the world!" };
	char arr2[] = {
     "################################" };
	int left = 0;
	int right = strlen(arr1) - 1;

	while (left <= right) {
    
		arr2[left] = arr1[left];
		arr2[right] = arr1[right];
		printf("%s\n", arr2);
		Sleep(1000);// Sleep for a second 
		system("cls");// Clear the screen 
		left++;
		right--;
	}
	printf("%s\n", arr2);

	return 0;
}

5. Write code to achieve , Simulate user login scenarios , And can only log in three times ; Only three passwords are allowed , If the password is correct, the login is successful ; If all three inputs are wrong , Then exit the program .

int main() {
    
	int i = 0;
	// Assume the correct password is 123456
	char password[20] = {
     0 };

	for (i = 0; i < 3; i++) {
    
		printf(" Please input a password ：");
		scanf("%s", password);
		// Comparison of two strings , Out of commission ==, You should use strcmp
		if (strcmp(password, "123456") == 0){
    
			printf(" Login successful \n");
			break;
		}
		else {
    
			printf(" Wrong password , Please re-enter ！\n");
		}
	}
	if (i == 3) {
    
		printf(" Three wrong passwords , Exit procedure \n");
	}
	return 0;
}