Arduino mega crashes while reading somewhat large .txt from SD - arduino

Question

I have an Arduino mega with an SD Shield and a GSM shield. I'm trying to send one sms to 200 numbers from a text file on the SD card, but the Arduino reboots every time I try to send to over 100 numbers. It doesn't crash when I try to send to 70 numbers. I only read one number at a time so I don't understand the problem. I'm pretty new to Arduino programming.
Please help me this is for a tournament. Here's the code:
#include <avr/pgmspace.h>
#include <SPI.h>
#include <SD.h>
#include <GSM.h>
#define PINNUMBER ""
GSM gsmAccess;
GSM_SMS sms;
// GSM
boolean notConnected;
//char input;
//byte input2;
//char txtContent[200];
byte i = 1;
byte f = 0;
boolean sendit;
//char senderNumber[11];
const String stopp PROGMEM = "Stopp";
//SD
char numbers[11];
//char nmbr;
int l = 0;
//Optimizing
const char q PROGMEM = '\xe5'; // å
const char w PROGMEM = '\xe4'; // ä
const char e PROGMEM = '\xf6'; // ö
const char r PROGMEM = '\xc5'; // Å
const char t PROGMEM = '\xc4'; // Ä
const char y PROGMEM = '\xd6'; // Ö
void setup() {
// txtContent[0] = '\0';
i = 0;
pinMode(53, OUTPUT);
Serial.begin(115200);
// Serial.begin(4800);
Serial.println(F("Connecting to GSM..."));
notConnected = true;
while (notConnected) {
if (gsmAccess.begin(PINNUMBER) == GSM_READY) {
notConnected = false;
}
else {
Serial.println(F("Not Connected"));
delay(1000);
}
}
Serial.println(F("GSM Ready"));
if (!SD.begin(4)) {
Serial.println(F("Error with SD card"));
return;
}
Serial.println(F("SD Ready"));
delay(1000);
Serial.println(F("Write your sms and end it with * and press Send"));
Serial.flush();
}
void loop() {
char txtContent[300];
if (Serial.available() > 0 && !sendit) {
byte input2;
input2 = (int)Serial.read();
txtContent[i] = (char)input2;
if (txtContent[i] == '{') {
txtContent[i] = q;
}
else if (txtContent[i] == '}') {
txtContent[i] = w;
}
else if (txtContent[i] == '|') {
txtContent[i] = e;
}
else if (txtContent[i] == '[') {
txtContent[i] = r;
}
else if (txtContent[i] == ']') {
txtContent[i] = t;
}
else if (txtContent[i] == ';') {
txtContent[i] = y;
}
i++;
if (input2 == '*') {
// Remove the * from text.
for (int j = 0; j < sizeof(txtContent); j++) {
if (txtContent[j] == '*') {
txtContent[j] = '\0';
//Serial.println(txtContent);
}
}
sendit = true;
Serial.flush();
}
else {
sendit = false;
Serial.flush();
}
}
else if (sendit && txtContent[0] != '\0') {
int txtCount = 0;
// else if(sendit){
Serial.println(F("Sending please wait..."));
// Serial.flush();
File myFile;
myFile = SD.open("numbers.txt");
char input;
if (myFile) {
// if (myFile.available()) {
while(myFile.available()){
input = (char)myFile.read();
if (input == ',') {
sms.beginSMS(numbers);
sms.print(txtContent);
// sms.beginSMS("0704941025");
// sms.print("yo");
delay(30);
sms.endSMS();
delay(30);
Serial.println(numbers);
Serial.flush();
// Serial.flush();
for (int j = 0; j < sizeof(numbers); j++) {
if (numbers[i] != '\0') {
numbers[j] = '\0';
}
}
f = 0;
}
else {
numbers[f] = input;
f++;
}
}
myFile.close();
Serial.println(F("All texts have been sent."));
Serial.flush();
} else {
Serial.println(F("error opening numbers.txt"));
}
for (int j = 0; j < sizeof(txtContent); j++) { // Clear text
txtContent[j] = '\0';
}
i = 0;
sendit = false;
}
else {
// delay(1000);
if (sms.available()) {
char senderNumber[11];
sms.remoteNumber(senderNumber, 11);
if (sms.peek() == 'S') {
Serial.print(F("Detta nummer har skickat Stopp: "));
Serial.println(senderNumber);
}
sms.flush();
Serial.flush();
// sendit = false;
}
}
}

Answer 1

Arduino is a strange ground for me but if that is anything like C, then i risk saying sizeof(numbers) will likely return 44, because you're asking for the size of an array in bytes, this probably means your for loop will iterate up to numbers[43] when numbers[] length is 11. Consider this instead:
for (int j = 0; j < sizeof(numbers)/sizeof(numbers[0]); j++) {
Same goes for all the other times you check for the size of an array in this code.
Also, do double check your textfile to ensure its really written in your expected format: 11 numbers then a comma, with no exception. You should maybe try to figure out if f went past 11 digits before hitting a comma and "Fail gracefully" with an error message.