Segmentation Fault: 11 C sometimes - c

Question

I'm trying to run a program in C on my mac that asks the user to input a set of names. The program then sorts and capitalizes all the names and prints them capitalized and sorted. It then allows the user to search for a name. However, most of the time (but not every time) I try to run the code it returns a segmentation fault: 11 error. My guess is that the problem has something to do with fgets or my array but I don't really know.
Here's my code:
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#define SIZE 50
#define LENGTH 50
#define TRUE 1
#define FALSE 0
void printList(char names[SIZE][LENGTH], int length);
void toUpperCase(char names[SIZE][LENGTH], int length);
void sort(char names[SIZE][LENGTH], int length);
void startSearch(char names[SIZE][LENGTH], int length);
int binSearch(char names[SIZE][LENGTH], int l, int r, char x[LENGTH]);
int main(void){
char names[SIZE][LENGTH]; //stores the list of names
printf("Enter student names (q to stop)...\n");
int i = 0;
do {
printf("Student name #%d: ", i);
fgets(names[i], LENGTH, stdin); //fill the list of names
int len = strlen(names[i])-1; //fgets includes \n character
if(names[i][len] == '\n') //if the last character is \n
names[i][len] = '\0'; //change it to \0
if(strcmp(names[i], "") == 0)
printf("Invalid input: Type a name\n");
else
i++;
}
while(strcmp(names[i-1],"q")!=0 && i<SIZE); //Stop collecting names after input "q"
//or if the names array is full
int length = i-1; //# of names in the names array
sort(names, length);
toUpperCase(names, length);
printList(names, length);
startSearch(names, length);
printf("Done!\n");
return 0;
}
//Converts all the names in the names array to upper case
void toUpperCase(char names[SIZE][LENGTH], int length){
for(int i = 0; i < length; i++){
for(int j = 0; names[i][j]!='\n'; j++){
if(islower(names[i][j]))
names[i][j] = toupper(names[i][j]);
}
}
}
//sorts the names in the names array (bubble sort)
void sort(char names[SIZE][LENGTH], int length){
int i, j;
char temp[LENGTH];
for (i = 0; i < length-1; i++)
for (j = 0; j < length-i-1; j++)
if (strcmp(names[j],names[j+1])>0){
strcpy(temp, names[j]);
strcpy(names[j], names[j+1]);
strcpy(names[j+1], temp);
}
}
//prints the names in the names array
void printList(char names[SIZE][LENGTH], int length){
printf("Student list: [\n");
for(int i = 0; i < length; i++)
if(i == length-1)
printf("\t%s\n", names[i]);
else
printf("\t%s,\n", names[i]);
printf("]\n");
}
//The first method for searching the list
void startSearch(char names[SIZE][LENGTH], int length){
char search[LENGTH];
while(strcmp(search, "q")!=0){
printf("Enter a name to search (q to exit): ");
fgets(search, LENGTH, stdin); //gets the name to search
int len = strlen(search)-1;
if(search[len] == '\n')
search[len] = '\0';
if(strcmp(search, "q") == 0) //if entered value is q
break; //break out of the loop
//Since the list is all upper case change the search value to upper case
for(int j = 0; search[j]!='\n'; j++){
if(islower(search[j]))
search[j] = toupper(search[j]);
}
printf("Searching for %s ...\n", search);
// if binSearch returns true then the item is in the list
if(binSearch(names, 0, length-1, search) == TRUE)
printf("%s is in the list!\n", search); /
else
printf("%s is NOT in the list!\n", search);
}
}
//binary search for the names array
int binSearch(char names[SIZE][LENGTH], int l, int r, char x[LENGTH]){
while (l <= r)
{
int m = l + (r-l)/2;
if(strcmp(names[m], x) == 0)
return TRUE;
if(strcmp(names[m], x) < 0)
l = m + 1;
else
r = m - 1;
}
return FALSE;
}

Answer 1

I assume you're using fixed arrays of SIZE and LENGTH for learning purposes. For actual string-related work, you'd do well to heed kpra's advice and using the more complex, but more powerful, pointers (allocating them and deallocating at need).
In your reading loop you kill all the "\n"'s replacing them with zeroes.
Yet in your toUppercase() code you look for a "\n" instead of a 0x0. This risks blowing the buffer:
//Converts all the names in the names array to upper case
void toUpperCase(char names[SIZE][LENGTH], int length){
for(int i = 0; i < length; i++){
for(int j = 0; names[i][j]!='\n'; j++){
// what happens here if \n is not found and j exceeds SIZE?
if(islower(names[i][j]))
names[i][j] = toupper(names[i][j]);
}
}
}
You could replace \n with 0x0, but I think a safer loop would be:
for(int j = 0; j < SIZE; j++) {
if (yourstring[j] == 0) {
break;
}
This way you're sure never to overshoot SIZE, and the cycle is ended anyway if the end of string is found. Notice that this '\n' comparison is used also in the search loop.