Create a file or go to line n of that file - c

Question

I've been working on this C programming assignment and I just can't seem to find out why it is not behaving the way I expect it to be behaving. The program is supposed to run, and there are 3 possible options for commands 0, -n, and n, where n is a positive integer.
When I execute the program, and type 0 as the command (which should create a file if one has not already been created) it just loops back to asking me to enter a command.
The commands -n and n go to the line specified by n and seeks to it. n prints line n, whereas -n prints all lines from n onward until it can no longer read from the text file.
Would greatly appreciate it if somebody could give me a hint or two and steer me in the right direction.
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <stdlib.h>
#define BUFSIZE 256
#define LINESIZE 1024
int write(FILE *fp);
int grade_validation(int grade);
int id_validation(char studentid[]);
int display(FILE *fp, int cmd);
int display_all(FILE *fp, int cmd);
int main(int argc, char *argv[]) {
if(argc != 2) {
perror("invalid number of args");
return 1;
} else {
FILE *fp;
if((fp = fopen(argv[1], "wb+")) == 0) {
perror("fopen");
return 1;
}
write(fp);
fclose(fp);
}
return 0;
}
int write(FILE* fp) {
int grade;
char studentid[BUFSIZE];
char input[BUFSIZE];
int cmd;
while(1) {
printf("Input 0 to append, n to view, or -n to view all records starting from n.\n");
if(!fgets(input, LINESIZE, stdin)) {
clearerr(stdin);
return 0;
}
if((sscanf(input, "%d", &cmd) == 1)) {
if(cmd == 0) {
if((id_validation(studentid)) != 1 || (grade_validation(&grade) == -1)) {
continue;
}
fprintf(fp, "%s %3d ", studentid, grade);
} else if(cmd > 0) {
display(fp, cmd);
} else if(cmd < 0) {
display_all(fp, cmd);
}
}
}
}
int grade_validation(int grade) {
char input[BUFSIZE];
FILE *fp;
if(grade >= 0 && grade <= 100) {
return 1;
}
if(sscanf(input, "%d", &grade) == 1) {
if((grade_validation(grade)) == 1) {
if(fprintf(fp, "%3d", grade) == 0) {
return 0;
}
printf("Grade recorded successfully.\n");
return 1;
}
}
return 0;
}
int id_validation(char studentid[]) {
char input[BUFSIZE];
FILE *fp;
size_t i = 0;
if(strlen(studentid) == 9) {
for(i = 0; i < 9; i++) {
if(isdigit(studentid[i])) {
return 1;
}
}
}
if(sscanf(input, "%s", studentid) == 1) {
if((id_validation(studentid)) == 1) {
if(fprintf(fp, "%s", studentid) == 0) {
return 0;
}
printf("Student ID recorded successfully.\n");
return 1;
}
}
return 0;
}
int display(FILE *fp, int cmd) {
char studentid[BUFSIZE];
int grade;
if(!fgets(cmd, BUFSIZE, fp)) {
clearerr(stdin);
return 0;
}
fseek(fp, cmd, SEEK_SET);
fprintf(stderr, "%s %3d", studentid, grade);
}
int display_all(FILE *fp, int cmd) {
char studentid[BUFSIZE];
int grade;
if(!fgets(cmd, BUFSIZE, fp)) {
clearerr(stdin);
return 0;
}
fseek(fp, cmd, SEEK_SET);
while((sscanf(studentid, grade, "%s %3d", cmd)) != EOF) {
fprintf(stderr, "%s %3d", studentid, grade);
}
}

Answer 1

You're trying to validate the uninitialized studentid and grade.
Also, you pass &grade to grade_validation, which expects and integer.
This would cause a warning, which should make you figure out something is wrong. Always compile with warnings enabled, and treated as errors (in gcc, -Wall -Werror).