why do we have to add NULL to print a reserve string using pointer in C? -

this program in c print string in reverse using pointer. meanning of *pre='\0'?

#include <stdio.h> int main() {    char string[50],reserve[50];    char *ps = string;    char *pre = reserve;    int i=-1;    printf(" input string : ");    scanf("%s",string);    while(*ps)    {       ps++;       i++;    }    while(i>=0)    {       ps--;       *pre = *ps;       pre++;       --i;    }    *pre='\0';    printf(" reverse of string : %s\n\n",reserve);    return 0; } 

setting *pre='\0'; idiomatic way of adding nul-terminator end of char[] array. required c string type functions work: e.g. printf call %s specifier.