#include<stdio.h>
#include<stdlib.h>
//#include<string.h>
//every string in C read scanf("%s") gets() end with '\0'
char temp[20];
int length(char w[])//srtlen
{
	int i;
	i=0;
	while(w[i]!='\0')
	{
		i++;
	}
	return i;
}
//from=panos,to=koligas
char* string_copy(char *from,char *to)//strcpy
{
	int i=0,j=0;
	printf("\nentering string_copy:i=%d,j=%d",i,j);
	if(length(to)>length(from))//αν το μήκος του to einai megalytero apo to mikos toy from
	{
		printf("\nto=%d---from=%d",length(to),length(from));//ektypwsi twn mikwn to,from...
	    getchar();
	    
	    printf("\nbegin copy from to temp...");
	    //copy olo to from sto temp
	  	for(i=0,j=0;from[j]!='\0';i++,j++)
	  	{
	     	temp[i]=from[j];
		 	printf("\n1.%d=%c",i,from[j]);	
		 	getchar();
	  	} 	
	  	printf("\nafter copying from to temp...temp=%s",temp);//ektypwsi temp mexri stigmis
	  	getchar();
	  //i--;
	  
	  		for(j=length(from);to[j]!='\0';j++)//antigrafi twn ypoloipwn xaraktirwn toy <to> sto temp
	  		{
	  			temp[i++]=to[j];
	  		}
	        temp[i]='\0';
	  			printf("\nafter copying the rest of to temp=%s",temp);//printing again temp
	            getchar();
	  				i=0;
	  				j=0;
	  				printf("\n2");
	  				getchar();
	}
return temp;
}

void string_concat(char *to,char *from)//strcat
{
	int i=0;
	while(to[i++]!='\0')
	;;
	int j=0;
	i--;
	while(to[i++]=from[j++])
      ;;
}

int main()
{
	char w[20];
	printf("give a word up to 20 characters: ");
	gets(w);
	printf("\nyou gave: %s\nit contains: %d characters!!",w,length(w));
	getchar();
	system("cls");
	
	char w1[20];
	char *w2="koligas";
	printf("give a word up to 20 characters: ");
	gets(w1);//w1=panos
	w2=string_copy(w1,w2);//from=w1=panos,to=w2=koligas
	printf("\nmain---after copying: %s",w2);//w1="panos",w2="panosas";
	getchar();
	system("cls");
	
	if(length(w)+length(w2)<20)
	{
	string_concat(w,w2);
	printf("after concatanating: %s",w);
	getchar();
	system("cls");
	}
	return 0;
}