C - Invalid instruction 4 - c

Question

I am working on an app that generates then lists school records. But every time I run it keeps giving me a
illegal instruction: 4
This is very annoying and won't go away. How can I fix this issue? Its been keeping me awake all night I've been looking all over the internet and can't find a solution.
This is the code that I am using I'm thinking its something with the arrays
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include <time.h>
struct student{
char Name[15];
char Grade[5];
char Age[3];
};
void GenerateStudent(int numOfStudents){
//Setting struct
struct student sdv[numOfStudents];
//Setting Defult Values
char names[50][15] = {
"Daniel",
"Olivia",
"Blair",
"Charley",
"Tom",
"Jim",
"Peter",
"Liam",
"Tasha",
"Marissa",
"Alexa",
"Ben",
"Kylie",
"Jasmin",
"Jaz",
"Merik",
"Nathan",
"William",
"Lucas",
"Mason",
"Logan",
"Alexander",
"Jack",
"Owen",
"James",
"Oliver",
"Jackson",
"Carter",
"Ryan",
"Matthew",
"Emma",
"Ava",
"Sophia",
"Charlotte",
"Emily",
"Abigail",
"Chloe",
"Isabella",
"Avery",
"Ella",
"Lily",
"Amelia",
"Hannah",
"Sofia",
"Grace",
"Victoria",
"Maya",
"Audrey",
"Evelyn",
"Nolan"
};
char grades[5][5] = {"A","B","C","D","F"};
int ages[] = {5,6,7,8,9,10,11,12,13,14,15,16,17};
int nameNum,gradeNum,ageNum;
//Getting Rand seed using time
time_t t;
srand((unsigned) time(&t));
for(int i = 0;i < numOfStudents;i++){
//Generating Rand #
nameNum = rand() % 50 + 1;
gradeNum = rand() % 5 + 1;
ageNum = rand() % 13;
//Writing Values to Array
strcpy(sdv[i].Name, names[nameNum]);
strcpy(sdv[i].Grade, grades[gradeNum]);
sprintf(sdv[i].Age, "%d", ages[ageNum]);
}
//Make sure you make a file called student_records.txt so you get the output of this app
FILE * fpointer = fopen("school_records.txt", "a");
printf("Writing to file...\n");
for(int n = 0;n < numOfStudents;n++){
//Printing Records into the file
fprintf(fpointer, "Name: %s Age: %s Avg Grade: %s\n", sdv[n].Name,sdv[n].Age,sdv[n].Grade);
}
//Removing the file from memory and saving changes
printf("Done!\n");
fclose(fpointer);
};
void mainMenu(){
printf("---------------Main Menu---------------\n");
printf("█████▒▒ 1.Generate Students\n");
printf("█████▒▒ 2.Clear Records\n");
printf("█████▒▒ 3.Exit\n");
printf("---------------------------------------\n");
}
void genMenu(){
printf("-------------Generate Menu-------------\n");
printf("Enter # of records you want to make\n");
printf("---------------------------------------\n");
}
void cleanMenu(){
printf("--------------Clear Menu---------------\n");
printf("Are you sure that you want to delete\nall information from the file?\n[Y]es or [N]o\n");
printf("-------------------------------------\n");
}
int main(){
//Declaring Variables
//We cant leave this one unasigned just becuase it can cause an error if the use types 0
int recordRequests = 1;
int i,entOption;
int exitNum = 0;
while(exitNum == 0){
mainMenu();
printf("Enter Option: ");
scanf("%d", &entOption);
if(entOption == 1){
printf("\n\n\n");
genMenu();
printf("Enter Value: ");
scanf("%d", &recordRequests);
GenerateStudent(recordRequests);
}else if(entOption == 2){
char ans;
int loopExit = 0;
cleanMenu();
printf("Enter Value: ");
scanf("&c", ans);
if(ans == 'Y'){
printf("Cleaning file...\n");
FILE * fpointer = fopen("school_records.txt", "w");
//Printing Records into the file
fprintf(fpointer,"");
//Removing the file from memory and saving changes
fclose(fpointer);
printf("Clean sucsessful!\nReturning to menu...\n");
loopExit = 0;
}else if(ans == 'N'){
printf("Sending back to main menu...\n\n\n");
loopExit = 1;
}else{
printf("Invalid Option Please type Y for yes or N for no\n");
}
}
}
return 0;
}

Answer 1

I believe I was able to reproduce your problem. When I run your code on my Microsoft compiler, I get a "Run-Time Check Failure #4" complaining about stack corruption near the variable-length array. I was able to fix this by adding space for the terminating null character by changing char Age[2]; to char Age[3];, as has already been hinted by several other people in the comments section.
The problem was that the following line was accessing all three arrays out of bounds:
sprintf(sdv[i].Age, "%d", ages[ageNum]);
It is accessing the array sdv out of bounds, because i is in the range [0..numOfStudents], but it should be in the range [0..numOfStudents-1]. This can be fixed by replacing the line for(int i = 0;i <= numOfStudents;i++){ with for(int i = 0;i < numOfStudents;i++){.
It is accessing the array sdv[i].Age out of bounds. That array is declared as a char array of length 2. However, the maximum string length is 3. For example, the string "14" requires a char array of length 3 for storage, because it also requires space for the terminating null character. This can be fixed by replacing the line char Age[2]; with char Age[3]; in the declaration of the student struct.
It is accessing the array ages out of bounds, because ageNum is in the range [1..13], but it should be in the range [0..12]. This is because, in the programming language C, array indexes are 0-based, in contrast to some other programming languages, which have 1-based array indexes. This can be fixed by changing the line ageNum = rand() % 13 + 1 to ageNum = rand() % 13;. Also, the +1 must be removed for the same reason from the two lines above that line.
Most likely, what I described as #2 is causing the stack memory corruption. However, all three out of bounds array accesses cause undefined behavior, so theoretically, any one of these could be the problem.
Additonally, your program contains the following bug:
In the function main, you assign the value 0 to exitNum and then set the for loop condition so that it continues as long as exitNum stays 0. However, you never assign a different value to exitNum. Therefore, you effectively have an infinite loop, making it impossible to exit your program from the main menu.