implement Oblique projection of 3D objects

#include<stdio.h>
#include<math.h>
#include<graphics.h>
main()
{
int x1,y1,x2,y2,gd,gm;
int ymax,a[4][8];
float par[4][4],b[4][8];
int i,j,k,m,n,p;
double L1,phi;

a[0][0] = 100; a[1][0] = 100; a[2][0] = 100;
a[0][1] = 200; a[1][1] = 100; a[2][1] = 100;

a[0][2] = 200; a[1][2] = 200; a[2][2] = 100;
a[0][3] = 100; a[1][3] = 200; a[2][3] = 100;

a[0][4] = 100; a[1][4] = 100; a[2][4] = 200;
a[0][5] = 200; a[1][5] = 100; a[2][5] = 200;

a[0][6] = 200; a[1][6] = 200; a[2][6] = 200;
a[0][7] = 100; a[1][7] = 200; a[2][7] = 200;

phi = (double) (3.14*45.0)/180 ;
L1 = 0.5;


par[0][0] = 1; par[0][1] = 0;
par[0][2] = L1*cos(phi); par[0][3] = 0;

par[1][0] = 0; par[1][1] = 1;
par[1][2] = L1*sin(phi); par[1][3] = 0;

par[2][0] = 0; par[2][1] = 0;
par[2][2] = 0; par[2][3] = 0;

par[3][0] = 0; par[3][1] = 0;
par[3][2] = 0; par[3][3] = 1;

m=4; n=4; p=8;

for(i=0; i<m; i++)
for(k=0; k<p; k++)
b[i][k] = 0;

for(i=0; i<m; i++)
for(k=0; k<p; k++)
for(j=0; j<n; j++)
b[i][k] += (float)par[i][j] * a[j][k];
detectgraph(&gd,&gm);
initgraph(&gd,&gm, "c:\\tc\\bgi");
ymax = getmaxy();

/*- front plane display -*/

for(j=0;j<3;j++)
{
x1=(int) b[0][j]; y1=(int) b[1][j];
x2=(int) b[0][j+1]; y2=(int) b[1][j+1];
line( x1,ymax-y1,x2,ymax-y2);
}
x1=(int) b[0][3]; y1=(int) b[1][3];
x2=(int) b[0][0]; y2=(int) b[1][0];
line( x1,ymax-y1,x2,ymax-y2);

/*- back plane display -*/
setcolor(11);
for(j=4;j<7;j++)
{
x1=(int) b[0][j]; y1=(int) b[1][j];
x2=(int) b[0][j+1]; y2=(int) b[1][j+1];
line( x1,ymax-y1,x2,ymax-y2);
}
x1=(int) b[0][7]; y1=(int) b[1][7];
x2=(int) b[0][4]; y2=(int) b[1][4];
line( x1,ymax-y1,x2,ymax-y2);
setcolor(13);
for(i=0;i<4;i++)
{
x1=(int) b[0][i]; y1=(int) b[1][i];
x2=(int) b[0][4+i]; y2=(int) b[1][4+i];
line( x1,ymax-y1,x2,ymax-y2);
}
getch(); getch();
}