Exercise analysis summary

If you will It's better to start than to give up . Roman.

May we all have our own goals and are making unremitting efforts for them .

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1、 Implement case conversion

// Implement case conversion 
// utilize  getchar  Realization  ： Be careful   Cache space 

#include<stdio.h>
int main()
{
	char ch = 0;
	printf(" Please enter ：\n");
	while ((ch = getchar()) != EOF)
	{
		if ((ch >= 'a') && (ch <= 'z'))// Small to capital 
		{
			ch -= 32;
		}
		else if ((ch >= 'A') && (ch <= 'Z')) // Capitalize to lowercase 
		{
			ch += 32;
		}
		else
		{
			printf(" illegal input ！\n");
			continue;
		}
		getchar();// Clear cache 
		printf(" The result of the conversion is ：\n");
		printf("%c\n", ch);
	}
	return 0;
}

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2、 String inversion （ Don't use library functions Not in reverse order ）

// String inversion （ Don't use library functions   Not in reverse order ）

#include<stdio.h>
// Calculate string length 
int getlen(char ch[])
{
	int count = 0;
	while (*ch != '\0')
	{
		count++;
		ch++;
	}
	return count;
}

// Method 1 ： Non recursive implementation of inverse : Subscript 
void Fturn1(char ch[], int len)
{
	int left = 0;
	int right = len - 1;
	while (left < right) // Attention condition 
	{
		char tmp = ch[left];
		ch[left] = ch[right];
		ch[right] = tmp;
		left++;
		right--;
	}
	printf(" Method 1 ： Non recursive （ Subscript ） Realize inversion :\n");
	printf("%s\n", ch);// Note that the printing method does not require i Loop printing 
}

// Note the pointer method ！！
// Method 1 ： Non recursive implementation of inverse : The pointer 
void Fturn2(char* ch, int len)
{
	char* left = ch;
	char* right = ch + len - 1;
	while (left < right)
	{
		char tmp = *left;
		*left = *right;
		*right = tmp;
		left++;
		right--;
	}
	printf(" Method 1 ： Non recursive （ The pointer ） Realize inversion :\n");
	printf("%s\n", ch);// Note that the printing method does not require i Loop printing 
}

// Method 2 ： Recursive implementation of inverse : assignment \0 Law 
// Means of implementation ： Swap heads and tails +turn（ A string of characters in the middle ）
// Pay attention to this method ！！！

void turn(char* ch, int len)
{
	char tmp = *ch;
	*(ch) = *(ch+len-1);
	*(ch + len - 1) = '\0';
	// Recursion must have constraints ： The number in the middle is greater than or equal to 2
	len = (getlen(ch + 1));
	if (len >= 2)
	{
		turn(ch+1, len);
	}
	*(ch + len + 2 - 1) = tmp; // Notice here ！！！： Be sure to add. 2
}

int main()
{
	// Define a string 
	char ch[] = "abcdefgh";
	printf(" Original string ：%s\n", ch);
	// Calculate string length 
	int len = getlen(ch);
	// Inversion ： First and last characters are exchanged , Exchange in turn 
	// Print in reverse order ： Just print in reverse 
	
	// Method 1 ： Non recursive implementation of inverse 
	Fturn1(ch, len);// Subscript 

	char ch1[] = "abcdefgh";
	Fturn2(ch1, len);// The pointer 

	// Method 2 ： Recursive implementation of inverse 
	char ch2[] = "abcdefgh";
	turn(ch2, len);
	printf(" Method 2 ： Recursive implementation of inverse :\n");
	printf("%s\n", ch2);// Note that the printing method does not require i Loop printing 

	return 0;
}

Be careful ：

• Within the function strlen You can find the length of the string , however sizeof Can not be
• notes ：strlen Record only '\0' The number of characters before , however sizeof hold '\0' Also counted as characters , Calculate the length
• Note the use of recursion in the code part

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3、 Recursive implementation n Of k Power

// Recursive implementation n Of k Power 

#include<stdio.h>

double Power(int n, int k)
{
	// Three situations ：k  Greater than 0   be equal to 0   Less than 0
	if (0 == k)
	{
		return 1.0;
	}
	else if (k > 0)
	{
		return n * Power(n, k-1);
	}
	else
	{
		return (1.0 / Power(n, -k));// Note that  -k
	}
}

int main()
{
	int n = 0;
	int k = 0;
	printf(" Please input the base number n  And the index k：\n");
	scanf("%d %d", &n, &k);
	double put = Power(n, k);
	printf("%d Of %d The power result is ：%lf\n", n, k, put); // Be careful double  The corresponding is  %lf
	return 0;
}

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4、 distinguish The length of the array And String length

• String length strlen Yes. '\0' , Record the previous number of characters , encounter '\0' To stop counting
• Be careful strlen Acting on strings , Not an integer array
• example ：

char acX[] = “abcdefg”;
char acY[] = {‘a’,’b’,’c’,’d’,’e’,’f’,’g’};

• The length of the array ： about acX In terms of arrays ： a b c d e f g \0    common 8 Character length
•                     about acY  In terms of arrays ： a b c d e f g     common 7 Character length
• String length  ： strlen Calculation
•               about acX In terms of arrays ： a b c d e f g \0    common 7 Character length （ Calculation \0 Number of previous characters ）
•               about acY  In terms of arrays ： a b c d e f g  It didn't appear after \0 , namely ： Followed by random values , When will it appear \0 Unknown , That is, the string length is unknown

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5、 Function pursuit High cohesion and low coupling ： Functions should be as independent as possible , Single function

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