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

int Search(char * , char *);//查找函數,返回單詞的位置
void Exchange(char * , char * , char *); //替換函數

void main()
{
	char str[80];	//一段文字	
	char s1[80];	//查找的單詞
	char s2[80];	//替代單詞

	printf("Please input a string:");
	gets(str);

	printf("Please input a search string:");
	gets(s1);

	printf("Please input a substitute string:");
	gets(s2);

	Exchange(str,s1,s2);
	printf("the result:%s\n",str);
}

int Search (char * str , char * s1)
{
	int i=0,j=0;
	while(str[i]!='\0')
	{
	   if(s1[j] == '\0') 
		{
			return i-j;
		}
  	   if(str[i] == s1[j]) j++;  
   	   else	j = 0;
  	   i++;
	}
	return 0;
}

void Exchange(char * str , char * s1 , char * s2)
{
	int location;	//單詞的位置
	int length1,length2;
	int i;

	length1 = strlen(s1);
	length2 = strlen(s2);

	do
	{
		location = Search(str , s1);
		printf("%d\n",location);
		if (location > 0)
		{
			if (length1 <= length2)
			{
				for(i = strlen(str); i >= location + length1 ; i--)
					str[ i + length2 - length1 ] = str[ i ];
				for(i = location ; i < location + length2 ; i++)
					str[ i ] = s2[ i - location ];
			}
			else
			{
				for(i = location + length2; i <= strlen(str) ; i++)
					str[ i ] = str[ i + length1 - length2 ];
				for(i = location ; i < location + length2 ; i++)
					str[ i ] = s2[ i - location ];
			}
		}
	}while (location != 0);

}