Check whether an input string matches the pattern provided, in this case US phone number: (###) ###-#### where # is a number.

phone_number_validation.c

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

#define TRUE 1
#define FALSE 0

#define ZERO '0'
#define NINE '9'

#define TOTAL_LENGTH 14

// Types
#define PARA_START 0
#define PARA_END 1
#define NUMBER 2
#define DASH 3
#define SPACE 4

int is_phone_number(char *number) {
  int i;
  int len;
  int position_type[TOTAL_LENGTH] = {
    PARA_START,
    NUMBER,
    NUMBER,
    NUMBER,
    PARA_END,
    SPACE,
    NUMBER,
    NUMBER,
    NUMBER,
    DASH,
    NUMBER,
    NUMBER,
    NUMBER,
    NUMBER
  };

  len = strlen(number);

  if (len != TOTAL_LENGTH) {
    return FALSE;
  }

  for (i = 0; i < len; i++) {
    switch (position_type[i]) {
      case PARA_START:
        if (number[i] != '(') {
          return FALSE;
        }
        break;
      case PARA_END:
        if (number[i] != ')') {
          return FALSE;
        }
        break;
      case DASH:
        if (number[i] != '-') {
          return FALSE;
        }
        break;
      case SPACE:
        if (number[i] != ' ') {
          return FALSE;
        }
        break;
      case NUMBER:
        if (number[i] < ZERO || number[i] > NINE) {
          return FALSE;
        }
        break;
    }
  }

  return TRUE;
}

int main(int argc, char **argv) {
  int is_phone = is_phone_number(argv[1]);

  if (is_phone) {
    printf("The given number is a phone number.\n");
  } else {
    printf("The given number is not a phone number.\n");
  }
}

Check whether an input string matches the pattern provided, in this case US phone number: (###) ###-#### where # is a number.
Example:
(800) 123-4567 => true
(123) 000-0000 => true
(ABC) 123-AB12 => false
12345678 => false
ABC-123-123C => false