".exe has stopped working"

[jjbeast098]

I am pretty new to C++ and programming in general, so I decided to make a cipher program that changes each letter to the letter 4 spaces after it. I know its not well written and can be much better, but what I mainly need help with is that it's not running. I spent a while fixing errors, and it finally compiled, but now when I run it and enter what word I want to encrypt, it says, "cipher.exe has stopped working." If anyone can please tell me why this is happening and/or anything else to improve my poor coding, please let me know.

#include <iostream>
#include <string>
#include <sstream>
#include <map>
using namespace std;

string cipher(string msg, map<string,int> letters, map<int,string> nums){ //The function to cipher the statement has the maps in the parameters so that they can be used outside of the main function.
	stringstream ss;
	string b2;
	string ans[msg.length()]; //The list of characters(as strings) of the encrypted message.
	string c;
	for(int x = 0; x < msg.length(); x++){
		char b = msg[x];
		ss << b;
		ss >> b2; //Converts the char b to a string b2
		int d = letters[b2]; //d is the numerical value of b2
		d+=4; //adds 4 to d to encrypt the message
		if(d > 26){
			c = nums[d-26];
		}
		else{
			c = nums[d]; //c is set to the alphabetical value of d
		}
		ans[x] = c; //c is put into the list of charcters of the encrypted message
	}
}
int main(){
	map<string,int> letters; //A map of letters a-z with numeric values.
	letters["a"] = 1;
	letters["b"] = 2;
	letters["c"] = 3;
	letters["d"] = 4;
	letters["e"] = 5;
	letters["f"] = 6;
	letters["g"] = 7;
	letters["h"] = 8;
	letters["i"] = 9;
	letters["j"] = 10;
	letters["k"] = 11;
	letters["l"] = 12;
	letters["m"] = 13;
	letters["n"] = 14;
	letters["o"] = 15;
	letters["p"] = 16;
	letters["q"] = 17;
	letters["r"] = 18;
	letters["s"] = 19;
	letters["t"] = 20;
	letters["u"] = 21;
	letters["v"] = 22;
	letters["w"] = 23;
	letters["x"] = 24;
	letters["y"] = 25;
	letters["z"] = 26;
	map<int,string> nums; //A map of numbers 1-26 with alphabetical values.
	nums[1] = "a";
	nums[2] = "b";
	nums[3] = "c";
	nums[4] = "d";
	nums[5] = "e";
	nums[6] = "f";
	nums[7] = "g";
	nums[8] = "h";
	nums[9] = "i";
	nums[10] = "j";
	nums[11] = "k";
	nums[12] = "l";
	nums[13] = "m";
	nums[14] = "n";
	nums[15] = "o";
	nums[16] = "p";
	nums[17] = "q";
	nums[18] = "r";
	nums[19] = "s";
	nums[20] = "t";
	nums[21] = "u";
	nums[22] = "v";
	nums[23] = "w";
	nums[24] = "x";
	nums[25] = "y";
	nums[26] = "z";
	string msg;
	cout << "What would you like to encrypt?" << endl; 
	cin >> msg; //what is being encrypted.

	cipher(msg,letters,nums); //Calls the cipher function
}

[cire]

string ans[msg.length()]; //The list of characters(as strings) of the encrypted message.
This is not legal in C++. You may have some compiler extension enabled that allows it, nevertheless in C++ the size of an array must be specified by a compile time constant. (And why do you want an array of strings here anyway?)

However, I imagine the cause of your memory corruption is promising to return a string in cipher and not actually doing so.