Question

The code was to copy and concatenate strings widout using library functions.the code i used:

#include<stdio.h>
#include<conio.h>
#include<string.h>
#define MAX 100
char* newStrCpy(char string1[],char string2[])
{
        int i=0;
        while(string1[i]!='\0')
        {
            string2[i]=string1[i];
            i++;
        }
return (string2);
}
char* newStrCat(char destination[],char arr[])
{
int a=0;
int destlen=0;
while(destination[destlen]!='\0')
{
    destlen ++;
}
while(a<(MAX-destlen))
{
    destination[(destlen+a)]=arr[a];
    a++;
}
return destination;
}
void main()
 {
char string1[MAX],string2[MAX];
int i=0,j=0;
char bak[5]="\n is";
char som[50]=" the concatenated array.";
fflush(stdin);

printf("Enter a string:\n");
scanf("%[^\n]s",&string1);
newStrCpy(string1,string2);
printf("The copied string is:\n");
while(string2[i]!='\0')
{
    printf("%c",string2[i]);
    i++;
}
newStrCat(string2,bak);
newStrCat(string2,som);
printf("\nThe conctenated string is:\n");
while(string2[j]!='\0')
{
    printf("%c",string2[j]);
    j++;
}
fflush(stdout);
getch();
}

and the output i got:

Enter a string:
Welcome!!

The copied string is:

Welcome!!
he concatenated string is:
Welcome!!
is the concatenated string

Answer 1

You need to initialize your string2 array:

char string2[MAX] ={'\0'};

This ensures all members are set to \0_{[Ref #1]} and you don’t have to bother appending a \0 manually to your string array, after copying.
Currently, your string2 array is never null terminated and hence the while loop continues till it encounters a \0 and it outputs garbage which is not a part of your string.

Also on a side note,

fflush(stdin);

makes your program have the beast of Undefined Behavior, do not use it.
fflush() is guaranteed to work on output stream stdout.

---

_{[Ref #1]}
C99 Standard 6.7.8.21

If there are fewer initializers in a brace-enclosed list than there are elements or members of an aggregate, or fewer characters in a string literal used to initialize an array of known size than there are elements in the array, the remainder of the aggregate shall be initialized implicitly the same as objects that have static storage duration.