what's wrong with this code?????

[ej25]

#include <stdio.h> 
#include <stdlib.h>
#include <fcntl.h>             /* defines options flags */ 
#include <sys/types.h>     /* defines types used by sys/stat.h */ 
#include <sys/stat.h>        /* defines S_IREAD & S_IWRITE  */ 

int main( )
{
  FILE *fd;
  int fd2;
  int sec,quize; 
  char buffer[1024];
  char buffer2[1024];
  int a,b,n,c=0;
  int random[100][100];

 
  int i,Sum1,Sum2,ii;
  float aver1,aver2;
  int j;
  fd = fopen("input.txt","w+");
   
  printf("Enter number of sections:");
  scanf("%d",&sec);

  printf("Enter number of quizes in each section:");
  scanf("%d",&quize);
  c= sec*quize;

  random[c][10];

  for(a=0;a<c;a++){
    for(b=0;b<10;b++)
       random[a][b]=rand()%21;
  }
 
  for(b=0;b<10;b++){
    for(a=0;a<c;a++){
      fprintf(fd,"%d",random[a][b]);
      fprintf(fd,"\t");
    }
    fprintf(fd,"\n");
  }

  for(a=0;a<c;a++){
    for(b=0;b<10;b++)
      printf("random[%d][%d]=%d\n",a,b,random[a][b]);
  }
	
  fclose (fd);  
        
  fd = fopen("input.txt","r+");
  i=1;
  ii=0; 
  Sum1=0; 
  Sum2=0;
  j=0;
  for(j=0;j!=c;j++){
    printf("section number %d\n",j);
    while(ii!=10){
      fscanf(fd,"%d",&a);
      printf("a:%d\n",a);
      Sum1=Sum1+a;
      i=1;
      while(i!=c){
         fscanf(fd,"%d",&a);
         i++;
      }
      ii++;
    }
    printf("%d\n",Sum1);
    aver1 = Sum1 / (float) ii;
    printf("%f\n",aver1);
  }
  fclose(fd);   
  return (0);
}

[redhead]

#include <stdio.h> 
#include <stdlib.h>
#include <fcntl.h>            /* defines options flags */
#include <sys/types.h>     /* defines types used by sys/stat.h */
#include <sys/stat.h>       /* defines S_IREAD & S_IWRITE  */

int main( )
{
  FILE *fd;
  int fd2;
  int sec,quize; 
  char buffer[1024];
  char buffer2[1024];
  int a,b,n,c=0;
  int random[100][100];

 
  int i,Sum1,Sum2,ii;
  float aver1,aver2;
  int j;
  fd = fopen("input.txt","w+");
   
  printf("Enter number of sections:");
  scanf("%d",&sec);

  printf("Enter number of quizes in each section:");
  scanf("%d",&quize);
  c= sec*quize;


/* 
 * what should this do ?? 
 * you're not assigning anything to that 
 * position in the random array
 */

  random[c][10];

  for(a=0;a<c;a++){
    for(b=0;b<10;b++)
       random[a][ b]=rand()%21;
  }
 
  for(b=0;b<10;b++){
    for(a=0;a<c;a++){
      fprintf(fd,"%d",random[a][ b]);
      fprintf(fd,"\t");
    }
    fprintf(fd,"\n");
  }

  for(a=0;a<c;a++){
    for(b=0;b<10;b++)
      printf("random[%d][%d]=%d\n",a,b,random[a][ b]);
  }
	
  fclose (fd);  
        
  fd = fopen("input.txt","r+");
  i=1;
  ii=0; 
  Sum1=0; 
  Sum2=0;
  j=0;
  for(j=0;j!=c;j++){
    printf("section number %d\n",j);
    while(ii!=10){
      fscanf(fd,"%d",&a);
      printf("a:%d\n",a);
      Sum1=Sum1+a;
      i=1;
      while(i!=c){
         fscanf(fd,"%d",&a);
         i++;
      }
      ii++;
    }
    printf("%d\n",Sum1);
    aver1 = Sum1 / (float) ii;
    printf("%f\n",aver1);
  }
  fclose(fd);   
  return (0);
}

First of all, what should it do..
A small test run of your code gives:

redhead@ask{57} ~> gcc -Wall -o te test.c
test.c: In function `main':
test.c:30: warning: statement with no effect // The random[c][10];
test.c:19: warning: unused variable `aver2'
test.c:14: warning: unused variable `n'
test.c:13: warning: unused variable `buffer2'
test.c:12: warning: unused variable `buffer'
test.c:10: warning: unused variable `fd2'
redhead@ask{58} ~> ./te
Enter number of sections:2
Enter number of quizes in each section:3
random[0][0]=1
random[0][1]=4
random[0][2]=9
random[0][3]=19
random[0][4]=8
random[0][5]=10
random[0][6]=10
random[0][7]=9
random[0][8]=15
random[0][9]=10
random[1][0]=2
random[1][1]=19
random[1][2]=20
random[1][3]=4
random[1][4]=20
random[1][5]=7
random[1][6]=3
random[1][7]=15
random[1][8]=16
random[1][9]=16
random[2][0]=17
random[2][1]=14
random[2][2]=12
random[2][3]=9
random[2][4]=2
random[2][5]=5
random[2][6]=5
random[2][7]=13
random[2][8]=1
random[2][9]=19
random[3][0]=5
random[3][1]=0
random[3][2]=3
random[3][3]=12
random[3][4]=17
random[3][5]=9
random[3][6]=1
random[3][7]=7
random[3][8]=16
random[3][9]=16
random[4][0]=15
random[4][1]=18
random[4][2]=12
random[4][3]=14
random[4][4]=20
random[4][5]=10
random[4][6]=20
random[4][7]=2
random[4][8]=2
random[4][9]=15
random[5][0]=17
random[5][1]=19
random[5][2]=7
random[5][3]=8
random[5][4]=8
random[5][5]=9
random[5][6]=11
random[5][7]=11
random[5][8]=1
random[5][9]=10
section number 0
a:1
a:4
a:9
a:19
a:8
a:10
a:10
a:9
a:15
a:10
95
9.500000
section number 1
95
9.500000
section number 2
95
9.500000
section number 3
95
9.500000
section number 4
95
9.500000
section number 5
95
9.500000
redhead@ask{60} ~> cat input.txt
1 2 17 5 15 17
4 19 14 0 18 19
9 20 12 3 12 7
19 4 9 12 14 8
8 20 2 17 20 8
10 7 5 9 10 9
10 3 5 1 20 11
9 15 13 7 2 11
15 16 1 16 2 1
10 16 19 16 15 10
redhead@ask{61} ~>

Seems to me, like it is saving all the random numbers that was calculated into the input.txt file, in your reading section you do have a small error tho, when reading from a filedescriptor you read one single line at a time, that means, when reading for section 1, you read every line in the file, leaving fd pointing at EOF for the following reads.
So in the end for the reads of 2 - 6 (in this small test case) you won't have any reads.
Either you should reconsider your readin section, where you most likely will read everything in, then sum up the sections, where number of sections can be decided by number of '\t' , and number of reads per section, which can be decided by number of '\n'.
Or you should consider the design of the write to input.txt, where you would have each line representing each sections, so an array like:

random[3][5] = {
                          {1, 2, 3, 4, 5},    
                          {10, 9, 8, 7, 6},                          
                          {1, 4, 6, 2, 8}
                        };
~> cat input.txt
1    2    3    4    5
10    9    8    7    6
1    4    6    2    8