Amazon online assessment coding question to find nth Geometric Progression

Question

Given the 2nd and 3rd term of a Geometric Progression. Find the nth term of it and round it off up to 3 decimal places.

we have to complete the following function:

char* nthTerm(double input1, double input2, int input3) {
    //your code here
}

input1 = 2nd term and input2 = 3rd term and both are between -2 to 2.
input3 = nth term to find and can be up to 100.

I was unable to convert the result from double to an array of char in the time limits. The test was on Mettl platform and I think I was unable to use to_string(), stringstream, etc. Although pow() function working fine.

e.g input1 = 1, input2 = 2, input3 = 4
  output = 4.0

Please, someone, help on how to solve this problem.

My approach but getting compilation error and wrong verdicts:

    double r = input2/input1;
    double a = input1/r;
    double ans = a * (double)pow(r, (double)(input3-1));
    char *result = new char[1000];
    // from here i tried so many thing like i used to_string, 
    // setprecision, maps, etc. But getting errors only.

Answer 1

You should first include what you tried as part of the question. Anyway, in order to convert a double value to char pointer, first you can use sprintf to convert it into a char array and then simply convert the result to char pointer. Example code below :

#include <stdio.h>

int main(void) {
    char charray[200];
    double num = 121.14;
    sprintf(charray, "%2.3f", num);
    char* c = &charray[0];
    printf("%s", c);
    return 0;
}