Programming learning records - Lesson 5 [branch and loop statements]

do while sentence

Execute statement first , Post judgment , It means executing at least once .

Two points search

Find an element in a sorted array , Because it's sorted , You can find it through two distributions , By judging the size of the middle elements of the array , Narrow the search , So back and forth , Until the corresponding element is found .

#include <stdio.h>
int main()
{
	int i = 0;int n = 0;int arr[100] = { 0 };
	printf(" Please enter the number of elements ( No more than 100)：\n");
	scanf("%d", &n);
	printf(" Please input elements from small to large ：\n");
	for (i = 0;i < n;i++) { scanf("%d", &arr[i]); }
	int target = 0;
	printf(" Please enter the element you want to find ：\n");
	scanf("%d", &target);
	int left = 0;
	int right = n - 1;
while (left <= right)  // Judge the condition , The left subscript cannot be larger than the right subscript .
{
	int m = (left + right) / 2;// Can also be used left+(right-left)/2, Used when the number is large 
	if(arr[m] < target) { left = m + 1; }// Move left subscript right , Narrow the scope of 
	else	if (arr[m] > target) { right = m - 1; }// Right subscript moves left , Narrow the scope of 
	else { printf(" Find success , The subscript is %d, Row of the first %d position .", m, m + 1);goto end; }
}
printf(" The element was not found ");
end:
return 0;
}

Guess the number game

Generation of random numbers , You need two functions ,rand() And srand(), You need to srand Pass a random number , Initialize random functions , So that rand() The function continuously outputs random numbers , Here to srand Pass the timestamp as a random number ,

srand((unsigned int)time(NULL)); To express to srand() Pass a time stamp after forced time conversion , There is no need to store pointer addresses , So to time() Store a null pointer NULL;

 Guess the number game 
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
void menu()
{
	printf("***** Guess the number game *****\n");
	printf("********************\n");
	printf("*******1- Start *******\n");
	printf("*******0- sign out *******\n");
	printf("********************\n");


}
void game()
{
	int s = rand()%100+1;// Operation of taking mold , Make the output random number controlled at 1-100;
	int guess = 0;
	while (1)// Put in a value that is always true , Control the continuation and jump out of the loop through the statements in the loop .
	{
		printf(" Please enter a number (1-100 Integers ):\n");
		scanf("%d", &guess);
		if (guess < s) { printf(" Guess a little \n");continue; }
		else if (guess > s) { printf(" Guess the \n");continue; }
		else { printf(" congratulations , Guessed it .\n"); break; }
	}
}
int main()
{
	srand((unsigned int)time(NULL));
	int input = 0;
	do// Put the menu and input and judgment into the cycle , So as to realize multiple operations .
	{
		menu();
		printf(" Please enter a command \n");
		scanf("%d", &input);
		switch (input)
		{
		    case 1: game();break;
			case 0:  printf(" Quit successfully \n");break;
			default: printf(" Invalid order \n");break;
		}

	} while (input);
		return 0;
}

Simulate user login

// Simulate user login 
//int main()
//{
//	char password[] = "liangzai";
//	char input[100] = " ";
//	int i = 0;
//	for (i = 0;i < 3;i++)
//	{
//		printf(" Please input a password :\n");
//		scanf("%s", &input);
//		if (strcmp(password, input) == 0) { printf(" Landing successful , Welcome, handsome boy ");break; }
//	}
//	if (i == 2) printf(" Diao Mao , Login without password ？");
//	return 0;
//}

The point to note here is char The definition of type , If defining a single character , It only needs char ch='a', That's a good definition , If you define a string , You need to define an array ,char ch[100]="abcedfg"; You can consider the size of the array by yourself , But make sure to prevent array overflow ,strcmp Function is a function that compares strings , The returned value is an integer , When the values are the same , return 0.strcmp(password, input) == 0 The string representing two character type variables is exactly the same . If not, a positive integer is returned .