Sorting and merging sequences of student records

/* sortmerge.c - Reads a file containing a sequence of records
*                representing students and places them into an
*                array table1. It does the same for a second file
*                placing result in table2. It then sorts table1 
*                and table2 in non descending order on the basis 
*                of their name fields. It now stores the merge of
*                the two sorted sequences in an array table3.
*                Finally it writes the result to a third file.
*                The names of the three files are passed as
*                command line parameters
*/           

#include <stdio.h>

#define SIZE 10
#define NAMESIZE 25

typedef struct {
char name[NAMESIZE];
int  midterm;
int final;
int homeworks;
} student;


void writeStudentArray(char filename[], student a[], int n)
/* n is the number of elements in the array a.
* filename is the name of the file where we will
* write.
*/
{
FILE *fd;  /* File descriptor used for filename */
int i;

if(n<=0)
return;
if((fd=fopen(filename,"w"))==NULL){
perror("fopen");
exit(1);
}
for (i=0;i<n;i++){
fprintf(fd,"%s %d %d %d\n",
a->name, a->midterm, a->final, a->homeworks);
a++;
}
fclose(fd);
}

int readStudentArray(char filename[], student a[], int nmax)
/* It reads up to nmax student records 
* from file filename and stores them in a.
* It returns the number of records actually read.
* WARNING: We assume that the name of the students contain no spaces.
*/
{
FILE *fd;  /* File descriptor used for filename */
int i=0;

if((fd=fopen(filename,"r"))==NULL){
perror("fopen");
exit(1);
}
while(fscanf(fd,"%s %d %d %d",
a->name, &a->midterm, &a->final, &a->homeworks)!=EOF){
if(++i==nmax)break;  /* We have filled up the table */
a++;
}
fclose(fd);
return i;
}

void sortStudentArray(student table[], int n){
/* It sorts in nondecreasing order on the basis of their
* names the first n records of table.
* WARNING: THIS IS A NULL STUB.
*/
}

int mergeStudentArray(student table3[], student table1[], int n1, 
student table2[], int n2){
/* It merges into table3 the first n1 student records of table1
* and the first n2 student records of table2. The records in
* table1 and table2 are sorted in nondecreasing order of their 
* name fields. It returns n1+n2.
* WARNING: THIS IS A STUB WHERE WE JUST COPY, NOT MERGE.
*/
int i,j=0;

for(i=0;i<n1;i++){
table3[j++] = table1[i];
}
for(i=0;i<n2;i++){
table3[j++] = table2[i];
}
return n1+n2;
}

int main(int argc, char *argv[]){
int n1,     /* Number of students in first sequence */
n2,       /* Number of students in second sequence */
n3;       /* Number of students in resulting sequence */

student table1[SIZE],  /* Students in first sequence */
table2[SIZE],        /* Students in second sequence */
table3[SIZE+SIZE];   /* Students in merged sequence */

if(argc!=4){
printf("Usage: %s unsfile1 unsfile2 outfile\n", argv[0]);
exit(0);
}
n1 = readStudentArray(argv[1],table1,SIZE);
sortStudentArray(table1,n1);
n2 = readStudentArray(argv[2],table2,SIZE);
sortStudentArray(table2,n2);
n3 = mergeStudentArray(table3, table1, n1, table2, n2);
writeStudentArray(argv[3],table3,n3);
}