This program works fine on my pc but when I submit it to a coding site, it says there is a segmentation fault. Please point out the error someone

Question

int main() {

  int n, found, query_no = 0;
  unsigned long int *phone;

  char **str, query[30], c;

  scanf("%d", &n);

  str = (char**) malloc(sizeof(char*) * n); //creating a pointer array of strings

  phone = (unsigned long int*) malloc(sizeof(unsigned long int) * n);
  for (int i = 0; i < n; i++) {
    str[i] = (char*) malloc(sizeof(char) * 30); //iitializing each pointer in arry
  }
  for (int i = 0; i < n; i++) {
    scanf("%s", *(str + i));
    scanf("%u", phone + i);
  }

  gets(query);
  char *p;
  p = query;

  while (*(p = gets(query)) != '\0')  //checks if blank line is entered
  {
    found = 0;
    for (int j = 0; j < n; j++) {
      /*two pointers are being passed here,*/
      /* one to the line entered and       */
      /* other to each character array pointed to by the pointer array*/
      if (strcmp(p, *(str + j)) == 0) {
        printf("%s", *(str + j));
        printf("=");
        printf("%u", *(phone + j));
        found = 1;
        break;
      }
    }
    if (found == 0) //if record not found, print so
      printf("Not found");
    printf("\n");
  }

The code inputs a phone book from user by first inputting the number of records to be inserted then in each new line a record is entered in the form of name number. Then the user searches for an unknown number records and we print the name and number if the records is found otherwise we print not found.

Source : Hackerrank 30 days of code Day 8 (I hope I am not violating any rules here, please tell me if I am)

Answer 1

the following proposed code:

1. cleanly compiles
2. performs the desired function
3. avoids any use of the heap allocation functions, like malloc()
4. allows easy modification to the actual MAX value for 'n' via a #define statement.
5. allows easy modification to the max name length via a #define statement.
6. consolidates the data representation into a simple struct.
7. avoids calling functions (I.E. gets()) that has been removed from the C standard.
8. because it is a 'Hackerrank' item, does not perform error checking.
9. stops when a blank line is read for a 'query'
10. note the use of size_t rather than int as the values are never <0

And now the proposed code:

#include <stdio.h>
#include <string.h>

#define MAX_NAMES 500
#define MAX_NAME_LEN 30

struct phoneBook
{
    char name[ MAX_NAME_LEN + 1]; // +1 to allow for NUL terminator
    unsigned long phone;
};

struct phoneBook myPhoneBook[ MAX_NAMES ];

int main( void )
{
    size_t n;

    scanf("%lu", &n);

    for (size_t i = 0; i < n; i++)
    {
        scanf( "%29s", myPhoneBook[i].name );
        char *newline;
        if( NULL != (newline = strchr( myPhoneBook[i].name, '\n' ) ) )
        {
            *newline = '\0';
        }
        scanf( "%lu",  &myPhoneBook[i].phone );
    }


    char query[MAX_NAME_LEN+2]; // +2 to allow for NUL byte and newline

    while ( fgets( query, sizeof(query), stdin ) )
    {
        if( query[0] == '\n' )
            break;

        char *newline;
        if( NULL != (newline = strchr( query, '\n' ) ) )
        {
            *newline = '\0';
        }

        size_t found = 0;

        for ( size_t j = 0; j < n; j++)
        {
            /*two pointers are being passed here,*/
            /* one to the line entered and       */
            /* other to each character array pointed to by the pointer array*/
            if (strcmp( query, myPhoneBook[j].name ) == 0)
            {
                printf( "%s", myPhoneBook[j].name );
                printf( "=" );
                printf( "%lu", myPhoneBook[j].phone );
                found = 1;
                break;
            }
        }

        if ( !found ) //if record not found, print so
            printf("Not found");
        printf("\n");
    }

    return 0;
}

Note: printf() and scanf() are SLOW. Suggest modifying the proposed code to use the following two functions, so never call printf() nor scanf():

void fastRead( size_t *a );
void fastWrite( size_t a );

inline void fastRead(size_t *a)
{
    int c=0;
    // note: 32 is space character
    // consume leading trash
    while (c<33) c=getchar_unlocked();

    // initialize result value
    *a=0;

    // punctuation parens, etc are show stoppers
    while (c>47 && c <58)
    { // then in range 0...9
        *a = (*a)*10 + (size_t)(c-48);
        c=getchar_unlocked();
    }
    //printf( "%s, value: %lu\n", __func__, *a );
} // end function: fastRead


inline void fastWrite(size_t a)
{
    char snum[20];
    //printf( "%s, %lu\n", __func__, a );

    int i=0;
    // decompose 'a' into char array
    do
    {
        // 48 is numeric character 0
        snum[i++] = (char)((a%10)+(size_t)48);
        a=a/10;
    }while(a>0);

    i=i-1; // correction for overincrement from prior 'while' loop

    while(i>=0)
    {
        putchar_unlocked(snum[i--]);
    }
    putchar_unlocked('\n');
} // end function: fastWrite