String arrays in C segmentation fault - c

Question

I'm trying to create an array of strings and pass strings to this array.
struct node {
int vertex_no;
};
int main() {
char city1[100], city2[100], buffer[999];
int distance;
FILE *fp;
fp = fopen("cities.txt", "r+");
if(fp == NULL)
perror("Error");
//Change - characters with space
while(1) {
char ch = fgetc(fp);
if(ch == '-') {
fseek(fp, ftell(fp)-1, SEEK_SET);
fputc(' ', fp);
}
if(ch == EOF)
break;
}
//Get to beginning of the file
fseek(fp, 0, SEEK_SET);
//Pass first line
fgets(buffer, sizeof(buffer), fp);
int i, j, v = 0;
char cities[100][100];
for(i = 0; i < 100; i++)
for(j = 0; j < 100; j++)
cities[i][j] = '\n';
int vertices = 0;
int add = 1;
//Find how many vertices we have
while(fscanf(fp, "%s %s %d", city1, city2, &distance) == 3) {
if(cities[0][0] == '\n') {
strcpy(cities[0], city1);
strcpy(cities[1], city2);
v = 2;
}
for(i = 0; cities[i][0] != '\n'; i++) {
//Search city1 inside cities array
if( strcmp(cities[i], city1) == 0 ) {
add = 0;
break;
}
//If not found add it to array
if(add) {
strcpy(cities[v], city1);
v++;
}
//Same search for city2
add = 1;
if( strcmp(cities[i], city2) == 0 ) {
add = 0;
break;
}
//If not found add it to array
if(add) {
strcpy(cities[v], city2);
v++;
}
}
}
for(i=0;cities[i][0] != '\n';i++)
printf("City no.%d = %s\n", i, cities[i]);
printf("Last city1, city2 and distance: %s, %s, %d", city1, city2, distance);
return 0;
}
As a result I get
segmentation fault(core dumped)
When I try to do something like this
char *test = NULL;
strcpy(test, "hello");
return 0;
I get the same segmentation fault again. Although when allocate space like this:
char *test = (char *) malloc(100);
There is no problem. But when I do like this:
char test[100];
There is also no problem. So that's why I don't understand the reason of getting segmentation fault even tho I used
char strings[100][100];
instead of
char *strings[100];

Answer 1

Following allocates a single pointer and sets that pointer to point to a single array of 100 characters. I.E. no place to insert 100 city strings.
char *test = NULL;
strcpy(test, "hello");
return 0;
....
char *test = (char *) malloc(100);
....
Following declares an array of 100 bytes with no room for 100 city strings
char test[100];
Following declares an array of 100 character arrays, of which each array is 100 bytes long
char strings[100][100];
Following declares an array of 100 pointers to char, not 100 character strings. So you would need to 'malloc' room for each city string and insert that pointer into the appropriate offset into the array.
char *strings[100];