Subj : Dartmouth BASIC to C
To   : comp.programming
From : John Smith
Date : Sat Aug 06 2005 06:59 pm

Having nothing better to do on a Saturday morning, I was looking at 
Kemeny & Kurtz's 1964 manual for BASIC:

http://www.bitsavers.org/pdf/dartmouth/BASIC_Oct64.pdf

Below is a C port of the first example program given in the manual. Can 
it be improved while preserving, as much as possible, the structure of 
the original BASIC program?

/*
     A C port of the 1st program given in Kemeny & Kurtz's
     manual for 1964 Dartmouth BASIC. It solves a system of
     linear equations with three different right sides.

     (A1*X1) + (A2*X2) = B1
     (A3*X1) + (A4*X2) = B2

     The program in BASIC:

     10 READ A1, A2, A3, A4
     15 LET D = A1 * A4 - A3 * A2
     20 IF D = 0 THEN 65
     30 READ B1, B2
     37 LET X1 = (B1 * A4 - B2 * A2) / D
     42 LET X2 = (A1 * B2 - A3 * B1) / D
     55 PRINT X1, X2
     60 GOTO 30
     65 PRINT "NO UNIQUE SOLUTION"
     70 DATA 1, 2, 4
     80 DATA 2, -7, 5
     85 DATA 1, 3, 4, -7
     90 END
*/

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

int main(void)
{
     int idx, sys;
     double A1, A2, A3, A4;
     double D, X1, X2, B1, B2;

     double DATA[] = {-7.0, 5.0, 1.0, 3.0, 4.0, -7.0};
     A1 = 1;
     A2 = 2;
     A3 = 4;
     A4 = 2;

     D = A1 * A4 - A3 * A2;
     if(D == 0.0)
     {
         printf("no unique solution\n");
         exit(EXIT_FAILURE);
     }
     idx = sys = 0;
     for(sys = 0; sys < 3; sys++)
     {
         B1 = DATA[idx++];
         B2 = DATA[idx++];
         X1 = (B1 * A4 - B2 * A2) / D;
         X2 = (A1 * B2 - A3 * B1) / D;
         printf("%f %f\n", X1, X2);
     }

     return 0;
}

.