C program to implement array of structure 

   #include<stdio.h>
 
struct student {
   char name[20];
   char roll[20];
   int mks;
} std[10], temp;
 
void main() {
   int i, j, n,size;
    printf("nEnter number of students : n");
      scanf("%d",&size);
 
     n=size;
   for (i = 0; i < n; i++) {
      printf("nEnter %d student Name : ",i+1);
      scanf("%s", std[i].name);
      printf("nEnter %d student Roll no : ",i+1);
      scanf("%s", std[i].roll);
      printf("nEnter %d student marks : ",i+1);
      scanf("%d", &std[i].mks);
      printf("n");
   }
    n=size;
   for (i = 1; i < n; i++)
      for (j = 0; j < n - i; j++) {
         if (strcmp(std[j].roll, std[j + 1].roll) > 0) {
            temp = std[j];
            std[j] = std[j + 1];
            std[j + 1] = temp;
         }
      }
 
   for (i = 0; i < n; i++) {
      printf("n%st%st%d",std[i].name,std[i].roll,std[i].mks);
   }
   getch();
}