string rotation by r places - c++

Question

I'm trying to rotate my string with 'r' places but facing some problem.The following is my code(function).Please help.
For eg: hello coding. after r=3 should become ng.hello codi.
void fnc(){
char a[100],key;
int n,r,i,t=1,total=0,count,x;
cin>>n; //no. of test cases
while(t<=n){
cin>>r; //no. of rotations
cin.get();
cin.get(a,100);
for(i=0; a[i]!= '\0'; i++){
//cout<<a[i];
total++;
}
cout<<total;
for(i=0; i<r; i++){
key = a[total-1];
cout<<"key: "<<key<<endl;
for(i=total-2; i>=0; i--){
a[i+1] = a[i];
}
a[0] = key;
}
for(i=0; a[i]!= '\0'; i++){
cout<<a[i];
}
///cout<<a<<endl;
t++;
}
}

Answer 1

Here is a way of doing this using only iterators:
#include <string>
#include <iostream>
using namespace std;
int mod(int a, unsigned int b) {
int ret = a % b;
return ret>=0 ? ret : b + ret;
}
string rotate(const string sentence, int rotation) {
rotation = mod(rotation, sentence.size());
string rotatedSentence;
for(auto itr=sentence.begin(); itr < sentence.end(); ++itr) {
if (distance(sentence.begin(), itr) < rotation) {
rotatedSentence.push_back(*(itr + sentence.size() - rotation));
} else {
rotatedSentence.push_back(*(itr - rotation));
}
}
return rotatedSentence;
}
int main() {
const string sentence = "hello coding.";
cout << sentence << endl;
cout << rotate(sentence, 3) << endl; //prints ng.hello codi
return 0;
}