Whats wrong with my code? The backwards loop doesnt work (Option 2) - slider

Question

The option (2) crashes/overloads my coding software, it has the same code as option (1), does anybody know why its doing it and how to fix it?
#include "aservelibs/aservelib.h"
#include <stdio.h>
#include <math.h>
int length();
float mtof(int note);
int main() {
// do while the user hasnt pressed exit key (whatever)
int control[8] = {74, 71, 91, 93, 73, 72, 5, 84};
int index;
int mod;
float frequency;
int notes[8];
int response;
mod = aserveGetControl(1);
// ask backwards, forwards, exit
// SCALING
// (getControl(75) / ((127 - 0) / (1000 - 100))) + 100;
while(true) {
printf("Run Loop Forwards (1), Backwards (2), Exit (0)\n");
scanf("%d", &response);
if(response == 1) {
while(mod == 0) {
for(index = 0; index < 8; index++) {
notes[index] = aserveGetControl(control[index]);
frequency = mtof(notes[index]);
aserveOscillator(0, frequency, 1.0, 0);
aserveSleep(length());
printf("Slider Value:%5d\n", notes[index]);
mod = aserveGetControl(1);
}
}
} else if(response == 2) {
// here is the part where the code is exactly
// the same apart from the for loop which is
// meant to make the loop go backwards
while(mod == 0) {
for(index = 8; index > 0; index--) {
notes[index] = aserveGetControl(control[index]);
frequency = mtof(notes[index]);
aserveOscillator(0, frequency, 1.0, 0);
aserveSleep(length());
printf("Slider Value:%5d\n", notes[index]);
mod = aserveGetControl(1);
}
}
} else if(response == 0) {
return 0;
}
}
}
int length() {
return (aserveGetControl(75)/((127.0 - 0) / (1000 - 100))) + 100;
}
float mtof(int note) {
return 440 * pow(2, (note-69) / 12.0);
}

Answer 1

Your for loops aren't exactly the same.
The first option goes through { 0, 1, ..., 7 }
The second option goes through { 8, 7, ..., 1 }
Notice also that control[8] is undefined (0..7). So when it tries to reference this location the application runs into an error.
Change the second for loop to
for (index = 7; index >= 0; index--) {
...
}