字符串库函数

#include <iostream>
using namespace std;

int strlenn(const char* str)
{
	int i=0;
	while (str[i]!=0) i++;
	return i;
}
int strcmp(const char* s1,const char* s2)
{
	int len1=strlenn(s1);
	int len2=strlenn(s2);
	for (int i=0;i<len1 && i<len2 ; ++i)
	{
		if(s1[i]<s2[i]) return -1;
		if(s1[i]>s2[i]) return 1;
	}
	
	if(len1 < len2) return -1;
	if(len1 > len2) return 1;
	return 0;
}
int strcopy(char* s1,const char* s2)
{
	//int len1=sizeof(s1)/sizeof(s1[0]);
	int len2=strlenn(s2);
	//if(len1 < len2+1) return -1;
	for (int i=0;i<len2;i++)
	{
		s1[i]=s2[i];
	}
	s1[len2]=0;
	return 0;
}
int struupr(char* s)
{
	int len=strlenn(s);
	for (int i=0;i<len;i++)
	{
		if(s[i]>='a' && s[i]<='z')
			s[i]=s[i]+'A'-'a';
	}
	return 0;
}
int strcatt(char* s1,const char* s2)
{
	int len1=strlenn(s1);
	int len2=strlenn(s2);
	for (int i=len1;i<len1+len2;++i)
	{
		s1[i] = s2[i-len1];
	}
	s1[len1+len2] = 0;
	return 0;
}
int main()
{
	char* s1="hello world";
	cout<<strlenn(s1)<<endl;

	cout<< strcmp("aabb","aabc")<<endl;

	char buf[30];
	strcopy(buf,"hello");
	
	strcatt(buf,s1);
	cout<<buf<<endl;
	
	struupr(buf);
	cout<<buf<<endl;
}