[C++知识库]C语言 字符串练习

C语言 字符串练习

将int类型数据转为字符串

#include <stdio.h>

char* itoa(char* str,int num)
{
	int tmp = abs(num),i = 0;
	while(tmp)
	{
		str[i++] = tmp%10+'0';
		tmp /= 10;
	}
	if(num < 0)
		str[i++] = '-'
	str[i] = '\0'	//字符串结束符
	char* s = str;	//字符串开始位置
	char* e = str+i-1;	//字符串结尾'\0'的前一位
	
	//将字符串反转
	while(s < e)
	{
		char t = *s;
		*s = *e;
		*e = t;
		s++,e--;
	}
	return str;
}

将句子倒序输出

#include <stdio.h>
#include <ctype.h>
#include <string.h>

void reverse(char* s,char* e)
{
	while(s > e)
	{
		char t = *s;
		*s = *e;
		*e = t;
		s++,e--;
	}
}

char* sentence_reverse(char* str)
{
	size_t len = strlen(str);
	//句子倒序
	reverse(str,str+len-1);
	/*
	  单词倒序 
	  句子中单词一般以空格区分，
	  但我们不知道单词的具体长度，
	  所以要去遍历句子找到空格位置
	*/
	char *s = str,*e = NULL;
	for(int i = 1; i <= len; i++)
	{
		//找到空格位置并将单词倒序
		if(!isalpha(str[i]) && '\''!=str[i])
		{
			e = str+i-1;
			reverse(s,e);
		}
		//每个单词的首字母前肯定不是字母，以此来确定单词首字母的起始位置
		if(isalpha(str[i])||('\''==str[i])&&(!isalpha(str[i-1])&&'\''!=str[i-1]))
		{
			s = str + i;
		}
	}
	return str;
}

两个数字字符串相加

#include <stdio.h>
#include <string.h>
#include <stdbool.h>

void resver(char* str)
{
	size_t len = strlen(str);
	for(int i = 0; i < len/2; i++)
	{
		char ch = str[i];
		str[i] = str[len-i-1];
		str[len-i-1] = ch;
	}
}

char* str_add(const char* s1,const char* s2,char* ret)
{
	const char* t1 = s1+strlen(s1)-1;
	const char* t2 = s2+strlen(s2)-1;
	const char *sl = NULL,*tl = NULL;

	char* tmp = ret;
	char carry = 0; // 进位
	while(true)
	{
		char s = (*t1-'0')+(*t2-'0')+carry;
		*tmp++ = s%10+'0';
		carry = s/10;
		if(t1==s1)
		{
			tl = t2;
			sl = s2;
			break;
		}
		if(t2 == s2)
		{
			tl = t1;
			sl = s1;
			break;
		}
		t1--,t2--;
	}
	while(tl != sl)
	{
		char s = (*tl-'0')+carry;
		*tmp = s%10+'0';
		carry = s/10;
		tl--,tmp++;
	}
	if(carry)
		*tmp++ = carry+'0';
	*tmp = '\0';
	resver(ret);
	return ret;
}