"this,is,an,demo,"

#include <stdio.h>

char *ReplaceString(const char *pInString, char *pOutString) 
{
	char *cp = pOutString ;
	//去除字串開頭的若干空格
	while(*pInString == ' ')
	{
		pInString ++;		
	}

	while(*pInString)
	{
		*cp = *pInString;
		cp++;
		pInString++;
	    
		if(*pInString == ' ')
		{
			*cp= ',';
		    cp++;			
			pInString++;
		}		
	}

	*cp = '\0';

	//最後一個字元用逗號結束
	if(*(cp - 1) != ',')
	{
		*cp  = ',';                      
		*(++cp) = '\0';
	}
	return pOutString;
}

int main()
{
	char *pin = "  This is a demo";
	char pout[100];
    ReplaceString(pin, pout);
	printf("%s \n", pin);
	printf("%s \n", pout);
	return 0;
}