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#include<stdlib.h>
#include<stdio.h>
#include<math.h>
#include<errno.h>
/*
* The purpose of this program is to simulate and record the average lifetimes
* of beetles on cardboard squares, suspended over vats of boiling oil. It takes
* in two parameters, both positive, long integers. The first integer refers
* to the length of one side of the cardboard square, in inches. The second
* refers to the number of beetles (number of times) with which to run this
* simulation.
*
* usage: ./beetle int int (./beetle square_size number_of_beetles)
*/
long double simulateLifetime(long int squareSize, long int beetleCount) {
/*
* simulateLifetime returns the collective lifetime of the beetles
* suspended over the vat of oil. If this function fails to simulate any
* beetles, it will return -1.
*
* This simulation places a beetle at the center of a cardboard square.
* The cardboard square is represented by a coordinate grid, with the origin
* being at the top-left corner, or the "home position". The
* beetle picks a random angle to move in, represented by random(),and moves
* forward 1 inch. This movement takes 1 second. The beetle waits 1 more
* second before starting the whole process over again. Once the beetle's
* coordinates move off the bounds of the coordinate grid, it "falls into
* the vat" and the simulation continues with the next beetle, decreasing
* the count.
*
* long int squareSize - represents the size of one side of the cardboard
* square.
*
* long int beetleCount - represents the number of beetles to simulate, or
* rather, the number of times to run the simulation.
*/
long double beetleX;
long double beetleY;
long double lifetime;
double angle;
long int count;
long int seconds;
lifetime = -1;
count = beetleCount;
seconds = 0;
while (count > 0) {
beetleX = squareSize / 2;
beetleY = squareSize / 2;
seconds = 0;
while (beetleX >= 0 && beetleY >= 0 && beetleX <= squareSize
&& beetleY <= squareSize) {
angle = random();
beetleX += cos(angle);
beetleY += sin(angle);
seconds++;
if (beetleX >= 0 && beetleY >= 0 && beetleX <= squareSize
&& beetleY <= squareSize) {
seconds++; // the beetle is resting but hasn't fallen off edge
}
}
lifetime += seconds;
count--;
}
return lifetime;
}
int main(int argc, char *argv[]) {
/*
* main sets up the beetle program. It reads the user's input and checks it
* to make sure that it is valid. It converts the input to values that the
* simulation function can use and then calls simulateLifetime(). main then
* prints the output to the console.
*/
long double lifetime;
long int squareSize;
long int beetleCount;
char *squareTest;
char *countTest;
// Check for improper number of arguments
if (argc != 3) {
fprintf(stderr, "beetle: usage: ./beetle int int\n");
exit(1);
}
errno = 0; // Reset error status
squareSize = strtol(argv[1], &squareTest, 10);
beetleCount = strtol(argv[2], &countTest, 10);
// Check for invalid input
if (squareTest == argv[1] || countTest == argv[2]) {
fprintf(stderr, "beetle: usage: ./beetle int int\n");
exit(1);
}
// Check for negative input
if (squareSize < 0 || beetleCount < 0) {
fprintf(stderr, "beetle: error: input must be positive integers\n");
exit(1);
}
// Check for overflow/underflow
if (errno == ERANGE) {
fprintf(stderr, "beetle: error: int too large\n");
exit(1);
}
// If no square to use for simulation then finish
if (squareSize == 0) {
fprintf(stderr, "No square given so lifetime is 0\n");
exit(0);
}
// If no beetles given then finish
if (beetleCount == 0) {
fprintf(stderr, "No beetles given, so lifetime is 0\n");
exit(0);
}
// Run simulation and check return value
if ((lifetime = simulateLifetime(squareSize, beetleCount)) == -1) {
fprintf(stderr, "beetle: error: beetles have achieved immortality!\n");
exit(1);
}
// Take the average of the beetles' lifetime and print the output.
lifetime = lifetime / beetleCount;
printf("%li by %li square, %li beetles, mean beetle lifetime is %.1Lf\n",
squareSize, squareSize, beetleCount, lifetime);
exit(0);
}
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