C++ Help. Arrays not working with integers - c++

Question

Here is my code: (C++)
#include <iostream>
#include <stdlib.h>
using namespace std;
int main(){
string sentence[9];
string word[9];
inb b[] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
int f = 0;
for (int i = 1; i <= 10; i += 1){
cin >> sentence[i - 1];
}
for (int a = 10; a > 1; a = a - b[f]){
b[f] = 0;
int f = rand() % 10;
b[f] = 1;
word[f] = sentence[f];
cout << world [f] << endl;
}
}
However, when I run this I get a "runtime error". That's it, no line, no further error. Nothing.
The Arrays in the bottom side of the code, like word[f] and b[f] do not work if I use f inside the "[]"'s.
When I change all the "f"'s with [1] to test the code, it works. But when I use "f"'s instead, it returns a runtime error.
Not sure if that is my compiler. But hey - I am a 2 day old C++ coder.

Answer 1

Your sentence is 9 "slots" big (addressed as sentence[0] to sentence[8]). You try to put something in the 10th slot (sentence[9]), which is a no-no.
(This pattern is repeated below with word.)
You most likely want to declare those arrays as 10-element ones.

Answer 2

That's because sentence and word contain nine units. But rand()%10 will produce 9, when you use word[f] = sentence[f], word[9] and sentence[9] are out of range. word[9] is the 10th element of array word.

Answer 3

There are several problems with your code. Firstly, sentence and word only have 9 entries, but you try to use 10. Array declaration is 1-based, e.g.
char foo[2];
declares two characters. However, they are numbered 0 and 1, thus
char foo[2];
foo[0] = 'a'; //valid
foo[1] = 'b'; //valid
foo[2] = 'c'; //very bad.
this problem might be obfuscated for you by the fact that you are making 'b' an auto-sized array.
The second problem is that you declare 'f' twice.
int f = 0;
for (int i = 1; i <= 10; i += 1){
and inside the loop
int f = rand() % 10;
b[f] = 1;
Your for loop, then, is broken:
for (int a = 10; a > 1; a = a - b[f]){
it uses the external 'f', which is always 0, to access element zero of b and subtract that from a.
Here is how I would write the code you're trying to write:
I honestly don't understand what your code is supposed to do, but here is how I might write a simpler version of the same thing:
#include <iostream>
#include <stdlib.h>
#include <array>
//using namespace std; <-- don't do this.
int main(){
std::array<std::string, 10> sentence; // ten strings
// populate the array of sentences.
for (size_t i = 0; i < sentence.size(); ++i) { // use ++ when ++ is what you mean.
std::cin >> sentence[i];
}
for (size_t i = 0; i < sentence.size(); ++i) {
size_t f = rand() % sentence.size(); // returns a value 0-9
std::cout << sentence[f] << " ";
}
std::cout << std::endl;
}
Requires C++11 (-std=c++11 compiler option). ideone live demo here