Check whether a date is valid in C or not?

Question

I need to check if a date is valid or not in C, and for this I will have a function called verificarData that will be passed to it the user input and will check whether or not it is a valid date.

But I’m in doubt, because I’ll have to break this to pieces data to check whether it contains :

1. Contains two bars between date

2. If the day is between 1 and 31.

3. If the month is between 1 and 12.

4. Year between 1900 and 2100

5. If month is 04, 06, 09 or 11, day can be maximum 30;

6. If month is 02, day can be maximum 28;

7. If year is leap and month is 02, day can be maximum 29.

Which is better to use in case ? Use vetor or even char and try to break the date and do the proper checks, and if I can use with char, how to break it into pieces to check ?

For example, if the user enters the following value :

Input : 20/03/2009

How can I break for you to stay, 20/, 03/ and 2009 separated so I can check ?

I also need to check if the day, month and year are numerical, but as I’m putting bars with numbers I can’t use the function isdigit to verify.

Example :

if(isdigit(data)) {
printf("São numéricos.");
}
else {
printf("Não são numéricos.");
}

But it returns as if they are not numbers even the user putting the day, the month and the year with numbers, because because of the bars, it returns as if it were a string. How can I check and return saying if they are numbers or not correctly ?

Answer 1

For example, if the user enters the following value :

Input : 20/03/2009

How can I break for you to stay, 20/, 03/ and 2009 separated so I can check?

Function

Use the functions below.

• strtok - breaks a string into tokens, given a specific delimiter (use /).

• strtol - converts a string to a long integer.

• strstr - finds the first occurrence of a specific substring in a string (use //).

• isdigit - checks if the character passed as argument is a digit.

Logic

Code base below. Also see working online here.

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

int verificarNumero(char *entrada) {
  int i;

  for (i = 0; entrada[i] != '\0'; i++)
  {
    if (entrada[i] != '/' && !isdigit(entrada[i]))
    {
      return 0;
    }
  }

  return 1;
}

int verificarData(char *entrada)
{
  const char substring[3] = "//";

  if (strstr(entrada, substring) != NULL)
  {
    return 0;
  }

  if (verificarNumero(entrada))
  {
    printf("São numéricos.\n");
  }
  else
  {
    printf("Não são numéricos.\n");
    return 0;
  }

  int i = 0;
  long data[3];
  const char delimitador[2] = "/";
  char *token = strtok(entrada, delimitador);

  // Alimenta o vetor de inteiros
  while (token != NULL)
  {
    data[i++] = strtol(token, NULL, 10);
    token = strtok(NULL, delimitador);
  }

  // Realize suas validações. Se alguma não for atingida, retorne '0'

  printf("Dia: %d\n", data[0]);
  printf("Mes: %d\n", data[1]);
  printf("Ano: %d\n", data[2]);

  // Caso contrário, retorne '1'

  return 1;
}

int main()
{
  char str[80];

  printf("Digite uma data: ");
  gets(str);

  printf("%d\n", verificarData(str));

  return(0);
}

Answer 2

Function to validate a date in the format dd/mm/yy: The string containing the date will have a fixed size whenever it is 11 counting with the control character ' 0', all that needs to be done is to convert the carcter representing the day/ month and the year and check its valid limits.

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

int valid(char *date)
{
int tmp=0,tmp1=0,tmp2=0,flag=0;
if(strlen(date)<=10){
tmp=(date[0]-'0')*10+(date[1] - '0');
if(tmp > 0 && tmp <32) flag++;
tmp1=(date[3]-'0')*10+(date[4]-'0');
if(tmp1 > 0 && tmp1 <13) flag++;
tmp2=(((date[6]-'0')*10+(date[7]-'0'))*10+(date[8]-'0'))*10+(date[9]-'0');
if(tmp2 > 2000) flag++;
}
return flag==3 ? 1 : 0;

}
  main()
  {
  char xx[20];
  gets(xx);
  printf("data valida %d?", valid(xx));
  }

Answer 3

Hello

I made a small example of how to validate data using if() The user input, function, check date checks if the data is correct; I hope I’ve helped with an example

#include <stdio.h>

int main()
{
    int dd, mm, yy;

    printf("Enter date (DD/MM/YYYY format): ");
    scanf_s("%d/%d/%d", &dd, &mm, &yy);

    //check year
    if (yy >= 1900 && yy <= 9999)
    {
        //check month
        if (mm >= 1 && mm <= 12)
        {
            //check days
            if ((dd >= 1 && dd <= 31) && (mm == 1 || mm == 3 || mm == 5 || mm == 7 || mm == 8 || mm == 10 || mm == 12))
                printf("Date is valid.\n");
            else if ((dd >= 1 && dd <= 30) && (mm == 4 || mm == 6 || mm == 9 || mm == 11))
                printf("Date is valid.\n");
            else if ((dd >= 1 && dd <= 28) && (mm == 2))
                printf("Date is valid.\n");
            else if (dd == 29 && mm == 2 && (yy % 400 == 0 || (yy % 4 == 0 && yy % 100 != 0)))
                printf("Date is valid.\n");
            else
                printf("Day is invalid.\n");
        }
        else
        {
            printf("Month is not valid.\n");
        }
    }
    else
    {
        printf("Year is not valid.\n");
    }

    return 0;
}