error: can't allocate region error code=3

I am really noob in programming, I know xD

I just started to learn, and this is my task - to make a simple text decoder.

So here it is:

 #include <iostream>
 #include <string>
 #include <vector>

using namespace std;
int main() 
{
string alp[26] =     {"a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"};
int key;
int let;
string mid;
int i;
int g;
int m;


cout << ("Enter key:");
cin >> key;

cout << ("Enter number of letters:");
cin >> let;
vector<string> out;

for(i = 1; i <= let; i++)
{
cout << ("Enter word by letters:") << endl;
cin >> mid;
    for(g = 0; g <= 26; g++)
    {

    if(mid == alp[g]){
        string sum;
        int sumlet = g + key;
        if(sumlet >= 26){
            int c = 26 - sumlet;
            sumlet = c * -1;
            sum = alp[sumlet];
            out.push_back(sum);
        }else if(sumlet << 0){
            int c = sumlet * -1;
            sumlet = 26 - c;
            sum = alp[sumlet];
            out.push_back(sum);
        }else
        {sum = alp[sumlet];
        out.push_back(sum);
        }


    }else{

    }

                }
}
cout << "Your text is: ";
for(m = 0; m <= let; m++ ){
    cout << out[m];
}
}

And it's returning me this after i enter all the letters:

Terminated due to signal: ABORT TRAP (6)

decoder(1367,0x7fffd9b9f3c0) malloc: * mach_vm_map(size=140734634131456) failed (error code=3) * error: can't allocate region *** set a breakpoint in malloc_error_break to debug libc++abi.dylib: terminating with uncaught exception of type std::bad_alloc: std::bad_alloc

What's the problem? Help please.