Strings and array of strings in C. Why using '\0'

Question

In this code below, in the while loop, what is '\0' in the condition?
#include <stdio.h>
typedef struct String{
char* word;
}String;
int length(String s){
int count=0;
while(s.word[count]!='\0'){
count++;
}
return count;
}
int main() {
String string[]={{"Werg0"},{"Joan"},{"Gohan"},{"Frieza"},{"Gandalf"}};
int value=sizeof(string)/sizeof(string[0]);
printf("sizeof(string): %ld, sizeof(string[0]): %ld\n",sizeof(string),sizeof(string[0]));
for(int i=0;i<value;i++){
printf("%s\n",string[i].word);
printf("length: %d\n",length(string[i]));
}
return 0;
}

Answer 1

the null character '\0' (also null terminator), is a control character with the value zero. the character has much more significance and it serves as a reserved character used to signify the end of a string,often called a "null-terminated string" .