[Aereshaa]

Here, let me put code tags around that, and indent it...

#include<stdio.h>
#include<conio.h>

void main(){
    int a[10][10],i,j,k,b,l,ans;
    clrscr();
    for(i=1;i<10;i++){
        for(j=1;j<10;j++){
             printf("a(%d,%d)\t",i,j);
             }
        printf("\n\n\n");
        }
    for(i=1;i<10;i++){ //input from user
         for(j=1;j<10;j++){
              printf(" a[%d,%d]?\n",i,j); // i hav used 0 to represent a blank box
              scanf("%d",&a[i][j]);
              }
         }
         for(i=1;i<10;i++){
              for(j=1;j<10;j++){
                   b=0;
                   if(a[i][j]==0){ //checks whether box is empty
                       end:
                       ans=0;
                       b=b+1; //gives a value to empty box
                       for(k=1;k<10;k++){
                            if(a[i][k]==b||a[k][j]==b){ //checks whether that value is already occupied in the same row and column
                                 ans=1;
                                 }
                            }
                       for(k=1;k<4;k++){
                            for(l=1;l<4;l++){
                                 if(a[3*(i/3)+l][3*(j/3)+k]==b){ //checks whether that value is occupied by the bigger box containing nine boxes
                                      ans=1;
                                      }
                                 }
                            }
                       if(ans=1){
                            goto end; //if yes, than it goes back and assign a higher value to the box
                            }
                        a[i][j]=b;
                        }
                   }
             }
        for(i=1;i<10;i++){ //prints the result
             for(j=1;j<10;j++){
                  printf("%d\t",a[i][j]);
                  }
             printf("\n");
        }
    getch();
    }

I'll take a look, and post again.