An old C code to display 256-color image in DOS and perform

/*
 C code to display 256-color image in DOS and perform Histogram Equalization
 Sandipan Dey
 BCSE, JU, Kolkata
 2003
*/

// MUST USE MEDIUM MEMORY MODEL
// USE 256 COLOR BITMAP FILE (WIDTH%4=0)
// INPUT IMAGE BEANS.BMP

#include <math.h>
#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
#include <graphics.h>
#include <string.h>
#define DEFAULT "output.bmp"
#define MAX 256
#define PI 3.14159

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

void Help() {
    printf("\nThis Program Takes an Image & Performs Histogram Equalization &");
    printf("\nStores it as another Image.");
    printf("\nTo Run the .Exe File:");
    printf("\nHEQ[.EXE] InputFileName [OutputFileName]");
    printf("\nThe following conditions must be satisfied:");
    printf("\n1)The Input Image must be an 8X8 (256-color) .BMP File");
    printf("\n2)No other Format currently supported.");
    printf("\n3)Default OutputFile is 'Output.BMP'");
    printf("\n4)The Input BMP & EGAVGA.BGI must be in the same Directory as the .EXE File");
    printf("\n5)N.B: For exact & correct Output All the Gray Levels [0..L-1]");
    printf("\n  MUST BE PRESENT in the RGB Palette of the Input BMP ");
    printf("\n  {L=Maximum Gray Level Possible}");
    printf("\n  Written By:-Sandipan Dey,BCSE-IV,Roll-99710,J.U.");
}

void main(int argc,char* argv[]) {
    FILE *fp=NULL,*fo=NULL;
    long int n[MAX]={0}, n1[MAX]={0};
    int c, type;
    char INPUTFILE[100], OUTPUTFILE[100];
    long int imgoffset=0;
    double sum=0, p[MAX]={0}, p1=0;
    strcpy(OUTPUTFILE,DEFAULT);
    clrscr();
    if(argc<=1) {
        printf("\nNo Input File!");
        getch();
        exit(0);
    }
    strcpy(INPUTFILE,argv[1]);
    if(argc>2 && strcmp(argv[2],"\0"))
        strcpy(OUTPUTFILE,argv[2]);
    if((fp=fopen(INPUTFILE,"rb"))==NULL) {
        printf("\n File Not Found!");
        fclose(fp);
        getch();
        exit(0);
    }    // File Not Found
    fo = fopen(OUTPUTFILE, "wb");
    if (fgetc(fp)!='B' || fgetc(fp)!='M') {      // Check Signature
        printf("\n Not a valid BMP File!!!");
        fclose(fp);
        fclose(fo);
        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);
    //printf(" %d",type);
    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!!!");
        fclose(fo);
        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);*/
    }
    fseek(fp,0,0);      // Goto Start of Bitmap
    while(!feof(fp)) {
        fputc(fgetc(fp),fo);
    }
    fclose(fp);
    fp=fopen(INPUTFILE,"rb");
    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,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;
        }
        ++n[c%MAX];
    }
    outtextxy(520,450,"Before");
    outtextxy(520,460,"Histogram");
    outtextxy(520,470,"Equalization");
    fclose(fp);
    getch();
    cleardevice();
    for(i=0;i<MAX;++i) {
        sum+=n[i];
    }
    for(i=0;i<MAX;++i) {
        p[i]=n[i]/(sum*1.0);
        p1=0;
        for(int j=0;j<=i;++j)
            p1+=p[j];
        n1[i]=(MAX-1)*p1;
    }
    fp=fopen(INPUTFILE,"rb");
    fseek(fp,imgoffset,0);
    fseek(fo,imgoffset,0);
    x=0;y=h;
    while(!feof(fp)) {
        c=fgetc(fp);
        putpixel(x,y,n1[c]/16);
        x=(x+1)%w;
        if(!x){--y;}
        fputc(n1[c],fo);
    }
    fclose(fp);
    fclose(fo);
    outtextxy(520,400,"After");
    outtextxy(520,410,"Histogram");
    outtextxy(520,419,"Equalization");
    outtextxy(520,445,"Sandipan Dey");
    outtextxy(520,455,"BCSE-IV");
    outtextxy(520,465,"Roll-99710");
    getch();
    cleardevice();
    //closegraph();
    gd=DETECT;
    initgraph(&gd,&gm,"");
    int xstart=10,ystart=470;
    line(xstart,ystart,620,ystart);
    line(xstart,ystart-470,xstart,ystart);
    char s[5];
    setcolor(14);
    for(i=0;i<MAX;++i) {
        line(xstart+2*i,ystart-5000*p[i],xstart+2*i,ystart);
        if(!(i%15)){
            setcolor(getmaxcolor());
            line(xstart+2*i,ystart-5,xstart+2*i,ystart+1);
            sprintf(s,"%d",i);
            outtextxy(xstart+2*i-7,ystart+2,s);
            setcolor(14);
        }
    }
    fflush(stdin);
    getch();
    for(i=0;i<MAX;++i)n[i]=0;
    fo=fopen(OUTPUTFILE,"rb");
    fseek(fo,imgoffset,0);
    while(!feof(fo)){
        c=fgetc(fp);
        ++n[c%MAX];
    }
    fclose(fo);
    sum=0;
    for(i=0;i<MAX;++i) {
        sum+=n[i];
    }
    for(i=0;i<MAX;++i)
    p[i]=n[i]/(sum*1.0);
    setcolor(12);
    for(i=0;i<MAX;++i)  {
        line(xstart+2*i,ystart-5000*p[i],xstart+2*i,ystart);
        if(!(i%15)){
            setcolor(getmaxcolor());
            line(xstart+2*i,ystart-5,xstart+2*i,ystart+1);
            sprintf(s,"%d",i);
            outtextxy(xstart+2*i-7,ystart+2,s);
            setcolor(12);
        }
    }
    getch();
    closegraph();
}