for loop: for (i=1;i<6;i++)
            {
             <statements> ;
             }
 example:
         void main()
         {                                 output: 1
          int a;                                   2
          for (a=1;a<5;a++)                        3
           printf ("%d\n",a);                      4
          }
 example:
         void main()
         {                                 output: 1      
           int a,b;                                12
           for (a=1;a<=5;a++)                      123
           {                                       1234
            for (b=1;b<=a;b++)
            printf ("%d",b);
            printf ("\n");
            }

example:
         void main()
         {
          int a,b,c;                            output:     1 
          for (a=1;a<=5;a++)                               11
          {                                               111
           for (b=1;b<=5-a;b++)                          1111
           printf (" ");                                11111
           for (c=1;c<=a;c++)
           printf ("%d",1);
          printf ("\n");
          }
         getch();
         }

example:
         void main()
         {
          int a,b,c;                            output:      1 
          for (a=1;a<=5;a++)                                1 1
          {                                                1 1 1
           for (b=1;b<=5-a;b++)                           1 1 1 1
           printf (" ");                                 1 1 1 1 1
           for (c=1;c<=a;c++)
           printf (" %d",1);
          printf ("\n");
          }
         getch();
         }

example:
         void main()
         {
          int a,b,c,d;                          output:     1 
          for (a=1;a<=5;a++)                               121
          {                                               12321
           for (b=1;b<=5-a;b++)                          1234321
           printf (" ");                                123454321
           for (c=1;c<=a;c++)
           printf ("%d",c);
           for (d=c-2;d>=1;d--)
           printf ("%d",d);
          printf ("\n");
          }
         getch();
         }

example:
         void main()
         {
          int a,b,c,d;                          output:     1 
          for (a=1;a<=15;a++)                              121
          {                                               12321
           for (b=1;b<=5-a;b++)                          1234321
           printf (" ");                                123454321
           for (c=1;c<=a;c++)                          12345654321
           {                                          1234567654321
            if (c>=10)                               123456787654321
            printf ("%d",c%10);                     12345678987654321
            else                                   1234567890987654321  -because c%10 for c=10 is 0
            printf ("%d",c);                      123456789010987654321 -because c%10 for c=11 is 1
            }                                    12....
           for (d=c-2;d>=1;d--)
           {
            if (d>=10)
            printf ("%d",d);
            else
            printf ("%d",d);
            }
          printf ("\n");
          }
         getch();
         }