/* REXX */	
ARG SRCHARG	/* Set search argument	*/

/*  File requirement: Sequential file where the search argument is 
unique within the file, and the file is sorted in ascending sequence by that field.	*/	
	
"ALLOC F(DD1) DA('TEST.FILE') SHR REUSE"                        /* Allocate sequential file */
"EXECIO * DISKR DD1 (STEM DD1. FINIS"                       	/* Read records into stem variables  */
	
DO UNTIL SRCHARG = "" | SRCHARG = EXIT	
	MIN = 0	               					/* Initialize lowest rec #  */
	MAX = DD1.0 + 1	     					/* Initialize highest rec #	*/
	MIDPOINT = MAX % 2   					/* Calculate midpoint of file  */

	DO UNTIL FILEARG = SRCHARG | MIDPOINT = MIN		/* Iterative loop	*/

	FILEARG = SUBSTR(DD1.MIDPOINT,1,4)			/* Set variable for search compare	*/
	SELECT
	WHEN SRCHARG < FILEARG THEN MAX = MIDPOINT		/* SRCHARG in lower half...reset MAX */
	WHEN SRCHARG > FILEARG THEN MIN = MIDPOINT		/* SRCHARG in upper half...reset MIN */	
	OTHERWISE NOP
	END  
	MIDPOINT = MIN + ((MAX - MIN) % 2)			/* Re-calculate midpoint */
	END 
	
	IF SRCHARG = FILEARG THEN SAY SRCHARG "FOUND"		/* Indicate a hit	*/
	ELSE SAY SRCHARG "NOT FOUND"     			/* Indicate a miss */

	SAY "Enter a new search argument"                       /* Prompt for a new search argument */              
        PULL SRCHARG   						/* Retrieve the new search argument */
END

EXIT