Program does not take input from user to loop itself again. - c

Question

I have this code down here and it working for calculating but it does not take the input of the user to do the loop again and calculate for the user again or cancel. the function is near the end with if(rank == 0) { ... }. I need help figure out what am I missing
#include <math.h> //include files
#include <stdio.h>
#include "mpi.h"
void printit()
{
printf("\n*********************************\n");
printf("Welcome to the pi calculator!\n");
printf("Programmer: K. Spry\n");
printf("You set the number of divisions\n");
printf("for estimating the integral: \n\tf(x)=4/(1+x^2)");
printf("\n");
printf("*********************************\n");
} //end printit
//function prototypes
int main(int argc, char* argv[])
{
double actual_pi = 3.141592653589793238462643;
//for comparison later
int n, rank, num_proc, i;
double temp_pi, calc_pi, int_size, part_sum, x;
char response = 'y';
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
MPI_Comm_size(MPI_COMM_WORLD, &num_proc);
if (rank == 0)
{
printit();
} /* I am root node, print out welcome */
while (response == 'y')
{
if (rank == 0)
{ /*I am root node*/
printf("__________________________________\n");
printf("\nEnter the number of intervals: (0 will exit)\n");
n = fgetc(stdin);
}
else
{
int_size = 1.0 / (double) n; //calcs interval size
part_sum = 0.0;
for (i = rank * n / num_proc; i <= (rank + 1)* n / num_proc; i += 1)
{ //calcs partial sums
x = int_size * ((double)i - 0.5);
part_sum += (4.0 / (1.0 + x*x));
}
temp_pi = int_size * part_sum;
//collects all partial sums computes pi
MPI_Reduce(&temp_pi,&calc_pi, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD);
if (rank == 0)
{ /*I am server*/
printf("pi is approximately %f", calc_pi);
printf(". Error is %f", fabs(calc_pi - actual_pi));
printf("\n");
printf("_______________________________________");
printf("\n");
}
} //end else
if (rank == 0)
{ /*I am root node*/
printf("\nCompute with new intervals? (y/n)\n");
response = fgetc(stdin);
}
} //end while
MPI_Finalize(); //terminate MPI
return 0;
}
The problem I have is with the if inside the loop while that ask user to Compute with new intervals and user will input Y or N to response. The problem is when users do input, it stop working and never loop.

Answer 1

It behave as it should from what you coded :-).
The comment from ptb is the answer of your question.... But lets do it :-).
while (response == 'y')
{
if (rank == 0)
{ /*I am root node*/
printf("__________________________________\n");
printf("\nEnter the number of intervals: (0 will exit)\n");
n = fgetc(stdin);
}
/* here we have to: broadcast to all processes the value of response
in fact all processes have to wait that root get the new value and then
get this value from the root. Fortunately MPI_Broadcast is a blocking
opperation, so no MPI_Barrier are needed...*/
MPI_Bcast(&n,1,MPI_INT,0,MPI_COMM_WORLD);
/* then your computation is done by every processes (in fact in your interval
boundaries you indeed take that process 0 has the first interval... i am not
sure your math a correct, I did not check them) */
int_size = 1.0 / (double) n; //calcs interval size
part_sum = 0.0;
for (i = rank * n / num_proc; i <= (rank + 1)* n / num_proc; i += 1)
{ //calcs partial sums
x = int_size * ((double)i - 0.5);
part_sum += (4.0 / (1.0 + x*x));
}
temp_pi = int_size * part_sum;
//collects all partial sums computes pi
MPI_Reduce(&temp_pi,&calc_pi, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD);
if (rank == 0)
{ /*I am server*/
printf("pi is approximately %f", calc_pi);
printf(". Error is %f", fabs(calc_pi - actual_pi));
printf("\n");
printf("_______________________________________");
printf("\n");
}
if (rank == 0)
{ /*I am root node*/
printf("\nCompute with new intervals? (y/n)\n");
response = fgetc(stdin);
}
/* here we have to: broadcast to all processes the value of response
in fact all processes have to wait that root get the new value and then
get this value from the root. Fortunately MPI_Broadcast is a blocking
opperation, so no MPI_Barrier are needed..., lol same than with n...*/
MPI_Bcast(&response,1,MPI_CHAR,0,MPI_COMM_WORLD);
} //end while
I did not try to compile... so there is maybe some typos...