#include<stdio.h>
#include<string.h>
#include<stdlib.h>

int main()
{
   int num_of_students=0;
   char input[100];
   int id[500];
   char names[500][50];
   double marks[500];
   double average_marks = 0.0;

   printf("Please enter the total number of students : ");
   gets(input);                       // Taking user input for number of students

   num_of_students = atoi(input);       // converting char to int

   for(int i=0;i<num_of_students;i++)
   {
       gets(input);

       char int_temp[20];
       int j;
       for(j=0;input[j]!=',';j++)
       {
           int_temp[j] = input[j];
       }
       int_temp[j] = '\0';
       id[i] = atoi(int_temp);
       j++;
       int k=0;
       for(;input[j]!=',';j++)
       {
           names[i][k] = input[j];
           k++;
       }
       names[i][k] = '\0';
       j++;

       char double_temp[20];
       k=0;
       for(;input[j]!='\0';j++)
       {
           double_temp[k++] = input[j];
       }
       double_temp[k] = '\0';
       marks[i] = atof(double_temp);

   }

   for(int i=0;i<num_of_students;i++)
   {
       average_marks += marks[i];

       printf("Student id : %d ,",id[i]);
       printf("Student name : ");
       for(int k=0;names[i][k]!='\0';k++)
       {
           if(names[i][k] >= 'a' && names[i][k] <= 'z')
           {
               printf("%c",names[i][k]-32);
           }
           else
           {
               printf("%c",names[i][k]);
           }
       }

       printf(", Student marks : %lf \n",marks[i]);
   }

   average_marks /= num_of_students;
   printf("Average marks : %lf\n",average_marks);


   while(1)
   {
       printf("Please enter a key for searching or press q/Q for exit : ");
       gets(input);

       if(input[1] == '\0' && (input[0] == 'q' || input[0] == 'Q'))
       {
           printf("Exiting the program");
           break;
       }
       double average = 0.0;
       int records_found = 0;

       for(int i=0;i<num_of_students;i++)
       {
           if(strstr(names[i],input) != NULL)
           {
               records_found++;
               average += marks[i];

               printf("Student id : %d ,",id[i]);
               printf("Student name : ");
               for(int k=0;names[i][k]!='\0';k++)
               {
                   if(names[i][k] >= 'a' && names[i][k] <= 'z')
                   {
                       printf("%c",names[i][k]-32);
                   }
                   else
                   {
                       printf("%c",names[i][k]);
                   }
               }

               printf(", Student marks : %lf \n",marks[i]);
           }

       }
       if(records_found != 0)
           average /= records_found;
       printf("Average marks : %lf\n",average);
   }

   return 0;
}

Ouput :

Please enter the total number of students : 5
1,amit sharma,97
2,shikar dhawan,95
3,rohit sharma,56
4,virat kohli,46
5,mahendra singh dhoni,99
Student id : 1 ,Student name : AMIT SHARMA, Student marks : 97.000000
Student id : 2 ,Student name : SHIKAR DHAWAN, Student marks : 95.000000
Student id : 3 ,Student name : ROHIT SHARMA, Student marks : 56.000000
Student id : 4 ,Student name : VIRAT KOHLI, Student marks : 46.000000
Student id : 5 ,Student name : MAHENDRA SINGH DHONI, Student marks : 99.000000
Average marks : 78.600000
Please enter a key for searching or press q/Q for exit : d
Student id : 2 ,Student name : SHIKAR DHAWAN, Student marks : 95.000000
Student id : 5 ,Student name : MAHENDRA SINGH DHONI, Student marks : 99.000000
Average marks : 97.000000
Please enter a key for searching or press q/Q for exit : q
Exiting the program