Sudoku solving algorithm C

 #include<stdio.h>
#include<stdlib.h>
#include<conio.h>
#include<time.h>
int a[9][9],b[9][9],r[60][2];
int row, col, icount, mode;
char solh;
void main()
{


void readvalues(void), display(void),generate(void);
int solve(),checkmat(), checkrow(), checkcolumn(),check(),isfixed();
int i,j,error;
char c;
clrscr();
printf("\t\t\t   SUDOKU SOLVER by:\n\n\t\t\t  \n\t\t\t   MCA-M.Tech CSE, Lovely Professional University\n\t\t\t   Email:@hotmail.com");
printf("\n\n\n\n\t\tEnter '1' to GENERATE SuDoKu Puzzle\n\n\t\tEnter any other key to SOLVE SuDoKu\n\n\n\n\t\tEnter: ");
scanf("%c",&c);
if(c=='1')
    {
    getchar();
    generate();
    if(solh=='y' || solh=='Y')
    readvalues();
    for(i=0;i<9 br="" i="">    for(j=0;j<9 br="" j="">    a[i][j]=b[i][j];
    clrscr();
    display();
    getchar();
    getchar();
    exit(0);
    }
clrscr();
printf("\n\n\t\t\tHOW TO ENTER ELEMENTS\n");
printf("\n\n1.Enter the elements by specifying the row and column number of\n  corresponding location");
printf("\n\n2.Each row and column start from 1 and end at 9 (not from 0 to 8)");
printf("\n\n3.After finishing entering the elements, enter zeroes (0)\n  for row or column");
printf("\n\n4.If an element entered in a wrong location has to be deleted,\n  enter zero in that location");
printf("\n\n\n\n\t\t\t  Enter any key to continue");
getchar();
read:
icount=0;
row=0; col=0;
for(i=0;i<9 br="" i="">for(j=0;j<9 br="" j="">a[i][j]=0;
for(i=0;i<60 br="" i="">    {
    r[i][0]=20; r[i][1]=20;
    }
    clrscr();
    readvalues();
    getchar();
    clrscr();
    ask:
    display();
    printf("\n\nEnter 'm' to MODIFY\nEnter 'r' to RE-ENTER\nEnter any other key for SUDOKU Solution: ");
    scanf("%c",&c);
    if(c=='r' || c=='R')
        {
        clrscr();
        goto read;
        }
    if(c=='m' || c=='M')
        {
        printf("\n\n");
        readvalues();
        clrscr();
        getchar();
        goto ask;
        }
    next:
    error=solve();
    clrscr();
    display();
    if(error==0)
    printf("\n\n\n\n\rNO SUOLUTION or TOO MANY MODIFICATIONS");
    cprintf("\n\n\n\n\n\rEnter c to continue and any other key to exit: ");
    scanf("%c",&c);
    if(c=='c')
    goto read;
    getchar();
}

/*FUNTION TO READ ELEMENTS*/

void readvalues()
{
int i=icount,j,x,y,chek;
void display(void);
int check(int,int);
clrscr();
do
{
display();
printf("\n");
row:
printf("\n\nEnter row: ");
scanf("%d",&r[i][0]);
if(r[i][0]==0)
    {
    r[i][0]=100; r[i][1]=100;
    break;
    }
if(r[i][0]>10 || r[i][0]<0 br="">    {
    printf("\nInvalid size\nEnter again");
    r[i][0]=20; r[i][1]=20;
    getchar();
    goto row;
    }
column:
printf("Enter column: ");
scanf("%d",&r[i][1]);
if(r[i][1]==0)
    {
    r[i][0]=100; r[i][1]=100;
    break;
    }
if(r[i][1]<0 i="" r="">10)
    {
    printf("\nInvalid size\nEnter again\n\n");
    r[i][0]=20; r[i][1]=20;
    getchar();
    goto column;
    }
r[i][0]=r[i][0]-1; r[i][1]=r[i][1]-1;
x=r[i][0]; y=r[i][1];
if(solh=='y' || solh=='Y')
for(j=0;j    {
    if(x==r[j][0] && y==r[j][1])
        {
        printf("This location is fixed and cannot be changed");
        goto row;
        }
    else
        r[i][0]=20; r[i][1]=20;
    }
scan:
printf("Enter the corresponding number: ");
scanf("%d",&a[x][y]);
if(a[x][y]==0)
    {
    for(j=0;j        {
        if(x==r[j][0] && y==r[j][1])
            {
            r[j][0]=20; r[j][1]=20;
            goto end;
            }
        if(solh=='y' || solh=='Y')
            {
            r[i][0]=20; r[i][1]=20;
            goto end;
            }
        }
    }
if(a[x][y]>9 || a[x][y]<=0)
    {
     printf("\nNumber out of range\nEnter again\n\n");
     a[x][y]=0;
     goto scan;
     }
else
{
chek=check(x,y);
if(chek==0)
    {
    printf("\nInconsistent number\nEnter again");
    a[x][y]=0; r[i][0]=20; r[i][1]=20;
    goto row;
    }
}
if(solh!='y' && solh!='Y')
    {
    icount++; i++;
    }
end:
clrscr();
}while(r[i-1][0]!=-1 || r[i-1][1]!=-1);
}

isfixed(int count, int m, int n)
{
int i;
for(i=0;iif(m==r[i][0] && n==r[i][1])
return(1);
return(0);
}

/*FUNCTION TO DISPLAY SUDOKU*/

void display()
{
int i,j,k,fixed;
gotoxy(6,0);
for(i=0;i<10 br="" i="">    {
    if(i%3==0)
        {
        textcolor(WHITE);
        if(i!=0)
        printf("\n");
        printf("\t\t");
        for(k=0;k<45 br="" k="">        cprintf("*");
        if(i==9)
        goto end;
        }
    if(i%3!=0)
        {
        textcolor(WHITE);
        printf("\n\t\t");
        printf("|\t\t\b|\t\t\b\b|\t\t\t\b\b\b\b|");
        printf("\n\t\t");
        }
    else
    printf("\n\t\t");
    for(j=0;j<9 br="" j="">        {
        if(j%3==0)
            {
            if(a[i][j]==0)
                {
                textcolor(WHITE);
                cprintf("|");
                for(k=0;k<4 br="" k="">                printf(" ");
                }
            else
                {
                textcolor(WHITE);
                cprintf("| ",a[i][j]);
                fixed=isfixed(icount,i,j);
                if(fixed==1)
                textcolor(LIGHTRED);
                else
                textcolor(LIGHTGREEN);
                cprintf("%d  ",a[i][j]);
                }
            }
        else
            {
            if(a[i][j]==0)
            for(k=0;k<5 br="" k="">            printf(" ");
            else
                {
                fixed=isfixed(icount,i,j);
                if(fixed==1)
                textcolor(LIGHTRED);
                else
                textcolor(LIGHTGREEN);
                cprintf("  %d  ",a[i][j]);
                }
            }
        }textcolor(WHITE);
        cprintf("\b|");
    }end:
}


int checkmat(int m, int n)
{
int x,y;
for(x=(m/3)*3;x<((m/3)*3+3);x++)
for(y=(n/3)*3;y<((n/3)*3+3);y++)
    {
    if(m!=x && n!=y)
    if(a[m][n]==a[x][y])
    return(0);
    }
return(1);
}


int checkrow(int m, int n)
{
int x;
for(x=0;x<9 br="" x="">    {
    if(x!=n)
    if(a[m][n]==a[m][x])
    return(0);
    }
return(1);
}


int checkcolumn(int m, int n)
{
int x;
for(x=0;x<9 br="" x="">    {
    if(x!=m)
    if(a[m][n]==a[x][n])
    return(0);
    }
return(1);
}

/*FUNCTION TO CHECK CONSISTENCY OF AN ELEMENT*/

int check(int m,int n)
{
int c;
c=checkmat(m,n);
if(c==1)
c=c*checkrow(m,n);
else
return(c);
if(c==1)
c=c*checkcolumn(m,n);
else
return(c);
return(c);
}

/*FUNCTION TO SOLVE SUDOKU*/

solve()
{
int i,m=0,n=0,number,c,fixed;

mainallot:

for(m=row;m<9 br="" m="">    {
    n=col;
    while(n<9 br="">        {
        number=1;
        fixed=isfixed(icount,m,n);
        if(fixed==0)
            {
            allot:
            a[m][n]=number;
            c=check(m,n);
            if(c==0)
                {
                number++;
                if(number>9)
                    {
                    a[m][n]=0;
                    if(n==0)
                        {
                        row=m-1; col=8;
                        if(row<0 br="">                        return(0);
                        goto backadjust;
                        }
                    else
                        {
                        row=m; col=n-1;
                        if(row<0 br="" col="">                        return(0);
                        goto backadjust;
                        }
                    }
                goto allot;
                }
            }
        n++;
        if(n>8)
        col=0;
        }
    }
return(1);

backadjust:

fixed=isfixed(icount,row,col);
if(fixed==0)
    {
    number=a[row][col];
    allot1:
    number++;
    a[row][col]=number;
    if(number>9)
        {
        a[row][col]=0;
        if(col==0)
            {
            row--; col=8;
            if(row<0 br="">            return(0);
            goto backadjust;
            }
        else
            {
            col--;
            if(col<0 br="">            return(0);
            goto backadjust;
            }
        }
    c=check(row,col);
    if(c==0)
    goto allot1;
    else
        {
        if(col==8)
            {
            row++;
            if(row>8)
            return(0);
            col=0;
            goto mainallot;
            }
        else
            {
            col++;
            if(col>8)
            return(0);
            goto mainallot;
            }
        }
    }
else
    {
    if(col==0)
        {
        row--; col=8;
        if(row<0 br="">        return(0);
        goto backadjust;
        }
    else
        {
        col--;
        if(col<0 br="">        return(0);
        goto backadjust;
        }
    }
}

/*FUNCTION TO GENERATE SODOKU*/

void generate()
{
int c,i,m,n,count=1,fixed,error;
char choice;
randomize();
generate:
for(m=0;m<9 br="" m="">for(n=0;n<9 br="" n="">a[m][n]=0;
for(i=0;i<60 br="" i="">    {
    r[i][0]=20; r[i][1]=20;
    }
clrscr();
printf("\n\n\n\n\t\tEnter your choice of difficulty");
printf("\n\n\n\t\t1.VERY EASY\n\n\t\t2.EASY\n\n\t\t3.MEDIUM\n\n\t\t4.HARD\n\n\n\t\tENTER: ");
scanf("%c",&choice);
switch(choice)
    {
    case '1': mode=34+random(4);
          break;
    case '2': mode=29+random(4);
          break;
    case '3': mode=27+random(2);
          break;
    case '4': mode=25+random(2);
          break;
    default : getchar();
              goto generate;
    }
a[0][0]=1+random(8); r[0][0]=0; r[0][1]=0;
for(count=1;count<10 br="" count="">    {
    choose:
    m=random(9); n=random(9);
    fixed=isfixed(icount,m,n);
    if(fixed==1)
    goto choose;
    r[count][0]=m; r[count][1]=n;
    allot:
    a[m][n]=1+random(9);
    if(a[m][n]==0)
    goto allot;
    c=check(m,n);
    if(c==0)
    goto allot;
    }
icount=count;
error=solve();
for(m=0;m<9 br="" m="">for(n=0;n<9 br="" n="">b[m][n]=a[m][n];
row=0; col=0;
for(i=0;i<60 br="" i="">    {
    r[i][0]=20; r[i][1]=20;
    }
if(error==0)
goto generate;
for(count=0;count    {
    choose2:
    m=random(9); n=random(5);
    fixed=isfixed(count,m,n);
    if(fixed==1)
    goto choose2;
    r[count][0]=m; r[count][1]=n;
    r[count+mode/2][0]=8-m;
    r[count+mode/2][1]=8-n;
    }
for(m=0;m<9 br="" m="">for(n=0;n<9 br="" n="">    {
    fixed=isfixed(mode,m,n);
    if(fixed!=1)
    a[m][n]=0;
    }
icount=mode;
clrscr();
display();
getchar();
printf("\n\n\nEnter 'y' to solve by yourself\nEnter 's' for solution\nEnter 'm' to generate more sudoku puzzles");
printf("\nAnd any other key to exit: ");
scanf("%c", &solh);
if(solh=='y' || solh=='Y' || solh=='s' || solh=='S')
return;
getchar();
if(solh=='m' || solh=='M')
goto generate;
exit(0);
}