c++ - warning: control reaches end of non-void function [-Wreturn-type]

Question

I am having a slight is regarding functions. I believe it is likely because I am not using them. My code is as follows:

/*date difference calculator*/

#include <stdio.h>

int main()
{
  int Date1 = 0, Date2 = 0, Dif, F, L, D1, D2, M1, M2, Y1, Y2;
  int x[13] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
  int y[13] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
  char A1, A2, B1, B2;

/*input first date*/

 fprintf (stderr , "Enter first date,in the form <day>/<month>/<year>  or <day>-<month>-<year>.
Where <day>,<month> and <year> are integers:
");
 (scanf("%i%c%i%c%i", &D1, &A1, &M1, &B1, &Y1));

/*check first date*/

 if (!(Y1 % 4)) x[2]=29;
 while ((Y1 < 1 || (Y1 > 9999)) || (M1 < 1 || M1 > 12) || (D1 < 1 || D1 > x[M1]) || (A1 != B1) || ((A1 != '/') && (A1 != '-'))) 
     {
       fprintf (stderr, "Incorrect format, re-enter date:
");
       scanf("%i%c%i%c%i", &D1, &A1, &M1, &B1, &Y1);
       if (!(Y1 % 4)) x[2]=29;
     }

/*print first date*/

 fprintf (stderr, "First date = %i%c%i%c%i
", D1 , A1 , M1 , B1 , Y1);

/*input second date*/

 fprintf (stderr , "Enter second date,in the form <day>/<month>/<year> or <day>-<month>-<year>.
Where <day>,<month> and <year> are integers:
");
 (scanf("%i%c%i%c%i", &D2, &A2, &M2, &B2, &Y2));

/*check second date*/

 if (!(Y2 % 4)) y[2]=29;
 while ((Y2 < 1 || (Y2 > 9999)) || (M2 < 1 || M2 > 12) || (D2 < 1 || D2 > y[M2]) || (A2 != B2) || ((A2 != '/') && (A2 != '-'))) 
     {
       fprintf (stderr, "Incorrect format, re-enter date:
");
       scanf("%i%c%i%c%i", &D2, &A2, &M2, &B2, &Y2);
       if (!(Y2 % 4)) y[2]=29;
     }

/*print second date*/

 fprintf (stderr, "Second date = %i%c%i%c%i
", D2 , A2 , M2 , B2 , Y2);

/*convert first date into days*/

 for (F = 1; Y1 > F ; F++) 
    {
     if (F % 4 == 0) (Date1 = Date1 + 366);
     else (Date1 = Date1 + 365);
    }
 for (L = 1; M1 > L ; L++) 
     Date1 = Date1 + x[L];
 Date1 = Date1 + D1;

/*convert second date into days*/

 for (F = 1; Y2 > F ; F++) 
    {
     if (F % 4 == 0) (Date2 = Date2 + 366);
     else (Date2 = Date2 + 365);
    }
 for (L = 1; M2 > L ; L++) 
     Date2 = Date2 + y[L];
 Date2 = Date2 + D2;

/*standard output*/

 Dif = Date2 - Date1;
 printf("
%i

" , Dif);

/*text output*/

 if (Date2 > Date1)  
    {Dif = Date2 - Date1;
    fprintf (stderr , "Indicating that the first date is %i days before second date.
" , Dif);}
 if (Date1 > Date2)  
    {Dif = Date1 - Date2;
    fprintf (stderr , "Indicating that the second date is %i days before first date.
" , Dif);} 
 if (Date1 == Date2)  
    fprintf (stderr , "Indicating that the first date is equal to second date.
"); 
}

When compiling using this: gcc -Wall -ansi date1.c -o date1 This occurs:

date1.c: In function ‘main’:
date1.c:70:1: warning: control reaches end of non-void function [-Wreturn-type]

Is there a simple fix for this or do I have to write my program to use functions propely? I am unable to change how I compile the code as it has to follow a set spec.

Apologies for the poor formatting of my question but this is my first time here and I was hoping to be able to do it alone.

Hope someone can help!

Answer 1

You just need to return from the main function at some point. The error message says that the function is defined to return a value but you are not returning anything.

  /* .... */
  if (Date1 == Date2)  
     fprintf (stderr , "Indicating that the first date is equal to second date.
"); 

  return 0;
}