this is what i have so far... i don't know how to begin my code for the "search" part.

int main(void)
{
	int i;
	student_t eee11[20];
	int a=0;
	int check1=0;
	int check2=0;
	FILE *in_file;


while(a!=1||a!=2||a!=3||a!=4){
printf("\n\t[1] Load file\n\t[2] Compute individual average\n\t[3] Compute class average\n\t[4] Exit\n\t[5] Search for a Student\nSelect a number:");
scanf("%d",&a);
getchar();

switch(a){
case 1:
	in_file=fopen("input_corrected.csv", "r");
	if(in_file==NULL){
		return 1;
	}
	else{
		for (i=0; i<20; i++)
		{
			eee11[i] = get_student(in_file);
		}
	}
	check1=1;
	break;


case 2:
	if(check1!=1){
		printf("INVALID INPUT!");
		break;
	}
	for (i=0; i<20; i++)
	{
		eee11[i].average = get_ave(eee11[i]);
		printf("The average of %s is %0.2f.\n", eee11[i].std_no, eee11[i].average);
		printf("press enter to proceed...");
		getchar();
	}
	check2=1;
	break;


case 3:
	if(check1!=1){
		printf("INVALID INPUT!");
		break;
	}
	get_class_ave(eee11, 20);
	break;

case 4:
	return 0;
	fclose(in_file);

case 5:
    //insert search code here

default:
	printf("Invalid input!\n");
	a=0;
	}
}
}

Just equivalent code that is human readable.

int main(void)
{
	int i;
	student_t eee11[20];
	int a=0;
	int check1=0;
	int check2=0;
	FILE *in_file;

	while(true) {
		printf(
			"\n"
			"\t[1] Load file\n"
			"\t[2] Compute individual average\n"
			"\t[3] Compute class average\n"
			"\t[4] Exit\n"
			"\t[5] Search for a Student\n"
			"Select a number:");
		scanf("%d\n",&a);

		switch(a){
		case 1:
			in_file=fopen("input_corrected.csv", "r");
			if(in_file==NULL)
				return 1;
			for (i=0; i<20; i++)
				eee11[i] = get_student(in_file);
			check1=1;
			break;
		case 2:
...

Still, the code above don't make any sense, unless you are targeting a specific data handling.
From here on you have somewhat unlimited number of choices:
a. Read each time all the file line by line: fgets, strstr(to find delimiter)
b. Read all the file into memory
- Store as is in a string
- Cut into fields and manage two-dimensional array
- Cut into fields and store array of structures
c. Employ Lex to cut delimiters
d. Employ ODBC with CSV driver
...

Notice that scanf is not good enough for production tools - you can't predict what garbage your user will put in.