1 files changed, 89 insertions, 0 deletions
diff --git a/reference/C/PROBLEMS/yesterday.c b/reference/C/PROBLEMS/yesterday.c
new file mode 100644
index 0000000..22095f2
--- /dev/null
+++ b/reference/C/PROBLEMS/yesterday.c
@@ -0,0 +1,89 @@
+/************************************************************************
+ * 
+ * Purpose: By default, display yesterdays date. 
+ *	    If a number is given on the command line, it is subtracted
+ *	    from todays date and the result printed.
+ *
+ * Author:  M.J. Leslie.
+ *
+ * Date:    10-Jan-95 
+ *
+ ************************************************************************/
+
+#include <time.h>
+#include <stdlib.h>
+#include <ctype.h>
+#include <string.h>
+
+#define  DAYS 1
+					/* Validate the command line 
+					 * parmeters 			*/
+int check_parm(int argc, char *argv[]);	
+
+/************************************************************************/
+
+main(int argc, char *argv[])
+   {
+
+   time_t seconds;
+   const int one_day = 86400;		/* Number of seconds in a day	*/
+   int days=DAYS;			/* Number of days to subtract.	*/
+
+
+					/* Checkout the cmd line parms  */
+   if (check_parm( argc, argv))	
+      {
+					/* Data is OK. 
+					 * Override the default.	*/
+      days = atoi(argv[1]);	
+      }
+                   			/* Get current calendar time.
+   					 * This is the number of seconds
+					 * since 1-jan-1970		*/
+   time(&seconds);
+
+					/* Subtract the required number
+					 * of days.			*/
+   seconds -= one_day*days;
+
+					/* Return the required date.	*/
+   printf("%s", ctime(&seconds));
+   
+					/* All done - time to go home.	*/
+   exit(1);
+   }
+
+/************************************************************************
+ *
+ *	Validate the data enter on the command line.
+ *
+ ************************************************************************/
+int check_parm(int argc, char *argv[])
+   {
+   if (argc > 1 )                       /* Q. Have we got parms?        */      
+     {
+     if ( !strcmp("-h", argv[1]))	/* Q. Help requested?		*/
+       {
+					/* Y.				*/
+       printf("%s will return the date of a passed day.", argv[0]);	
+       puts("\nFor example:");
+       printf("\t%s    \tReturns yesterdays date.\n", argv[0]);
+       printf("\t%s 1  \tReturns yesterdays date.\n", argv[0]);
+       printf("\t%s 365\tReturns the date one year ago.\n\n", argv[0]);
+       exit(0);
+       }
+                                        /* Do a simple check to validate
+                                         * the I/P data - not 100% reliable
+                                         */
+     if (!isdigit(*argv[1]))
+        {
+                                        /* Data naff.
+                                         * End the program.             */
+        printf("%s: Numeric value required.\n", argv[0]);
+        printf("\n\tTry: %s -h for some info.\n\n", argv[0]);
+        exit(0);
+        }
+     return(1);
+     }
+   return(0);
+   }