Your questions sound like homework questions. Why don't you put in the effort to actually learn the basics of C++ and then you might have an idea on where to begin?
int main() {
int count[10];
int x;
for (int c = 0; c < 1; c++)
count [c] = 0;
cout << "Enter 1 single digit integers: ";
for (int c = 1; c <= 1; c++) {
cin >> x;
count[x]++;
}
int min = count[0];
for (int c = 1; c <= 9; c++) {
if (count[c] < min) min = count[c];
}
bool found = false;
cout << "The digits ";
for (int c = 0; c <= 9; c++) {
if (count[c] == min) {
if (found) cout << "and ";
cout << c << " ";
}
found = true;
}
cout << "are least frequent.\n";
return 0;
}