string subscript out of range in C++ for Cowculations - c++

Question

Please help with debugging.
It gives me an error 'string subscript out of range error' after the fifth input.
I was unable to figure out what to change.
Here is the code:
#include <iostream>
#include <string>
#define N 100
int str2int(std::string input)
{
int num = 0;
for (int i = 0; i < input.length(); i++)
{
if (input[i] == 'V')
num *= 4 + 0;
else if (input[i] == 'U')
num *= 4 + 1;
else if (input[i] == 'C')
num *= 4 + 2;
else if (input[i] == 'D')
num *= 4 + 3;
}
return num;
}
int main(void)
{
int tablet = 0, num1 = 0, num2 = 0, ans = 0;
std::string cowNum1 = "", cowNum2 = "", result = "";
std::string operation = "";
std::cin >> tablet;
std::cout << "COWCULATIONS OUTPUT" << std::endl;
while (tablet--)
{
std::cin >> cowNum1 >> cowNum2;
num1 = str2int(cowNum1);
num2= str2int(cowNum2);
for (int oprt = 0; oprt < 3; oprt++)
{
std::cin >> operation[oprt];
switch (operation[oprt])
{
case 'A':
{
num2 += num1;
break;
}
case 'R':
{
num2 >>= 2;
break;
}
case 'L':
{
num2 <<= 2;
break;
}
case 'N':
default:
break;
}
}
std::cin >> result;
ans = str2int(result);
if (num2 == ans)
std::cout << "YES" << std::endl;
else
std::cout << "NO" << std::endl;
std::cout << "END OF OUTPUT" << std::endl;
}
return 0;
}
Question is from 377 - Cowculations
Sample Input
5
VVVVU
VVVVU
A
A
A
VVVVVVUV
VVCCV
VVDCC
L
R
A
VVVVUCVC
VVCCV
VVDCC
R
L
A
VVVVUCVV
VVUUU
VVVVU
A
N
N
VVVVVUCU
DDDDD
VVVVU
A
L
L
UVVVVVVV

Answer 1

You may not use the subscript operator for an empty string to change its value
std::cin >> operation[oprt];
At least you have to declare the object operation with the magic number 3 used in your for loop. For example
std::string operation( 3, '\0' );
Or
std::string operation;
operation.resize( 3 );
If you need to enter only one characters in a loop then an object of the type std::string is not required. You could just write
for (int oprt = 0; oprt < 3; oprt++)
{
char c;
std::cin >> c;
switch ( c )
{
case 'A':
{
num2 += num1;
break;
}
case 'R':
{
num2 >>= 2;
break;
}
case 'L':
{
num2 <<= 2;
break;
}
case 'N':
default:
break;
}
}