Old C code for bi-level display of an image in DOS

/*
 C program for bi-level display of an 8-bit BMP image in DOS
 Sandipan Dey
 BCSE, JU, Kolkata
 2003
*/

// MUST USE MEDIUM MEMORY MODEL
// INPUT IMAGE EINSTEIN.BMP GIRL.BMP: use a small image
#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
#include <graphics.h>
#include <string.h>
#define DEFAULT "output.bmp"
#define MAX 256

void fillmatrix(unsigned char a[8],int n) {
    int c=0,x,y;
    int k;
    while(c < n) {
        x=random(8);
        y=random(8);
        k=1;
        for(int j=0;j<y;++j,k<<=1);
        if(!(a[x] & k)){a[x]+=k;++c;}
    }
}

int FindAllRGB(int* b) {
    for(int i=0;i<MAX;++i)
    if(b[i]!=i)return 0;
    else return 1;
}

void main(int argc,char* argv[]) {
    FILE* fp=NULL;
    int c,type;
    char INPUTFILE[100];
    long int imgoffset=0;
    if(argc<=1) {
        printf("\nNo Input File!");
        getch();
        exit(0);
    }
    strcpy(INPUTFILE,argv[1]);
    if((fp=fopen(INPUTFILE,"rb"))==NULL) {
        printf("\n File Not Found!");
        fclose(fp);
        getch();
        exit(0);
    }    // File Not Found
    if(fgetc(fp)!='B' || fgetc(fp)!='M') {      // Check BMP Signature
        printf("\n Not a valid BMP File!!!");
        fclose(fp);
        getch();
        exit(0);
    }
    fseek(fp,10,0);                             // Find Offset of Data
    imgoffset=fgetc(fp)+(fgetc(fp)<<8)+(fgetc(fp)<<16)+(fgetc(fp)<<24);  // Data Offset
    fseek(fp,28,0);                             // Find No. of Bits to Represent a Pixel of the Bitmap
    type=fgetc(fp);
    switch(type) {
        case 1:printf("\n A Monochrome (1-Bit) Bitmap!");break;
        case 4:printf("\n A 16-Color (4-Bit) Bitmap!");break;
        case 8:printf("\n A 256-Color (8-Bit) Bitmap");break;
        default:printf("\n Not a 1,4 Or 8-Bit Bitmap!");break;
    }
    if(type!=8){
        fclose(fp);
        printf("\nAn 8-bit Bitmap expected!!!");
        exit(0);
    }
    fseek(fp,54,0);
    long int sum1=0;
    int r,g,bl,b[MAX]={0};
    for(int t=0;t<MAX;++t) {
        r=fgetc(fp);
        g=fgetc(fp);
        bl=fgetc(fp);
        sum1=(r+g+bl)/3;
        fgetc(fp);
        b[t]=sum1;
    }
    if(!FindAllRGB(b)){
        printf("\nNot All Gray Levels between 0 & %d are Present in RGB Palette!!!",MAX);
        getch();/*exit(0);*/
    }
    long int w,h;
    fseek(fp,18,0);
    w=fgetc(fp)+(fgetc(fp)<<8)+(fgetc(fp)<<16)+(fgetc(fp)<<24);
    h=fgetc(fp)+(fgetc(fp)<<8)+(fgetc(fp)<<16)+(fgetc(fp)<<24);
    fseek(fp,imgoffset,0);
    int gd=VGA,gm=VGAHI;
    long int x=0,y=h;
    struct palettetype pal;
    initgraph(&gd,&gm,"");
    getpalette(&pal);
    for (int i=0; i<16; i++)
    setrgbpalette(pal.colors[i],i*4,i*4,i*4);
    fseek(fp,imgoffset,0);
    while(!feof(fp)) {
        c=fgetc(fp);
        putpixel(x,y,c/16);
        x=(x+1)%w;
        if(!x){
            --y;
        }
    }
    outtextxy(500,450,"Gray Level Image");
    getch();
    cleardevice();
    unsigned char a[8]={0};
    fseek(fp,imgoffset,0);
    x=0;y=472;
    randomize();
    while(!feof(fp)) {
        for(int i=0;i<8;++i)
            a[i]=0;
        c=fgetc(fp);
        fillmatrix(a,c/8);
        for(i=0;i<8;++i) {
            for(int j=1,k=0;k<8;j<<=1,++k)
                if((a[i] & j)==j)
                    putpixel(x+k,y+i,WHITE);
        }
        x=(x+8)%(w*8);
        if(!x)y-=8;
    }
    outtextxy(485,420,"Bilevel Display");
    outtextxy(485,441,"Sandipan Dey");
    outtextxy(485,451,"BCSE-IV");
    outtextxy(485,461,"Roll-99710");
    outtextxy(485,471,"Jadavpur University");
    fclose(fp);
    getch();
    closegraph();
}