# pi in c with code examples

Pi is a mathematical constant that is commonly used in various fields, including engineering, physics, and mathematics. It is defined as the ratio of the circumference of a circle to its diameter and is represented by the Greek letter π. Pi is an irrational number and can be approximated by using various methods, such as the Monte Carlo method or the infinite series method.

C is a popular programming language that is widely used in various industries, including aviation, automotive, and medical. In this article, we will discuss how to calculate pi in C with code examples.

Calculating Pi in C using the Monte Carlo method

The Monte Carlo method is a statistical approach that involves generating random numbers within a given range and using them to estimate a quantity. The method can be used to calculate pi by generating random points within a unit square and counting the number of points that fall within the unit circle inscribed in the square.

The ratio of the number of points within the circle to the total number of points generated provides an estimate of pi. The following is an example code implementation of the Monte Carlo method in C:

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>

int main(){

double x, y, dist, pi_estimate;
int i, count = 0, num_iter = 1000000;

//random number generator seed
srand(time(NULL));

for(i=0; i<num_iter; i++){

```   //generate random numbers between 0 and 1
x = (double)rand()/RAND_MAX;
y = (double)rand()/RAND_MAX;

dist = sqrt(x*x + y*y);

//check if point is within the circle
if(dist <= 1){
count++;
}
```

}

//calculate pi estimate
pi_estimate = 4*(double)count/num_iter;

//print pi estimate
printf("Pi estimate using Monte Carlo method: %f
", pi_estimate);

return 0;
}

The above code generates one million random points within the unit square and counts the number of points that fall within the unit circle. The pi estimate is then calculated by multiplying the ratio of points within the circle to the total number of points generated by four. The pi estimate using this method may be different each time the code is executed due to the random generation of points.

Calculating Pi in C using Infinite Series

Pi can also be calculated using the infinite series method, which involves summing an infinite number of terms to get an approximation of pi. A famous example of this is the Leibniz formula, which is expressed as:

π/4 = 1 – 1/3 + 1/5 – 1/7 + 1/9 – …

The formula can be implemented in C as follows:

#include <stdio.h>

int main(){

double pi_estimate = 0, pi_actual = 3.14159265359;
int i, j, denominator = 1;

for(i=0; i<5000; i++){

```   if(i%2 == 0){
pi_estimate += 1.0/denominator;
denominator += 2;
}
else{
pi_estimate -= 1.0/denominator;
denominator += 2;
}
```

}

//multiply estimate by 4
pi_estimate *= 4;

//print estimate and actual pi value
printf("Pi estimate using infinite series: %f
", pi_estimate);
printf("Actual value of pi: %f
", pi_actual);

return 0;
}

The above code calculates pi using the Leibniz formula up to 5000 terms and multiplies the result by four. The pi estimate using this method gets closer to the actual value of pi as the number of terms in the series is increased.

Conclusion

In conclusion, pi is an essential mathematical constant used in various fields, and its value can be approximated using different methods. This article has demonstrated the calculation of pi in C using the Monte Carlo method and the infinite series method. The code examples provided can be used as a reference to calculate pi or as a starting point for more complex pi estimation algorithms.

Calculating Pi in C using the Monte Carlo method

The Monte Carlo method is a random-based approach that involves repeated sampling of random variables to calculate an unknown value. The method is particularly useful in cases where direct methods fail to provide accurate results, such as calculating pi. One of the most famous implementations of the Monte Carlo method for calculating pi is generating random points inside a unit square and counting those that fall within the inscribed unit circle. The more points are sampled, the more accurate the approximation of pi becomes, as shown by the following code example:

```#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#define NUM_SAMPLES 10000000

int main(){
int inside_circle = 0;
double x, y;

//seed random number generator
srand(time(NULL));

for(int i = 0; i < NUM_SAMPLES; i++){
//generate random 2D point
x = ((double)rand() / RAND_MAX) * 2 - 1; //x is in [-1, 1]
y = ((double)rand() / RAND_MAX) * 2 - 1; //y is in [-1, 1]

//check if point is inside the unit circle
inside_circle++;
}
}

//calculate pi estimate from sampled points
double pi_estimate = 4.0 * (double)inside_circle / NUM_SAMPLES;

printf("Pi estimate using Monte Carlo method: %f
", pi_estimate);

return 0;
}
```

The above code generates 10 million random 2D points and uses the proportion of those that are inside the unit circle to estimate the value of pi. The constant `RADIUS` is defined as half the diameter of the circle, and `NUM_SAMPLES` determines the number of points to be sampled in this implementation.

Calculating Pi in C using Infinite Series

Another way to calculate pi is by using infinite series, which relies on the mathematical properties of pi to derive formulas that converge to its value. Probably the most well-known of these formulas is the Leibniz formula shown in the previous example. However, it has a very slow convergence rate, meaning that a large number of terms must be summed to obtain satisfactory results. An alternative formula is the Gregory-Leibniz series:

```π/4 = 1 - 1/3 + 1/5 - 1/7 + 1/9 - 1/11 + ...
```

Despite its close relation to the former formula, the Gregory-Leibniz series converges much faster and requires far fewer terms to obtain the same accuracy. The following is an example implementation of this formula:

```#include <stdio.h>

#define NUM_TERMS 1000000

int main(){
double pi_estimate = 0, sign = 1;

for(int i = 0; i < NUM_TERMS; i++){
pi_estimate += sign / (2.0 * i + 1.0);
sign *= -1;
}

pi_estimate *= 4.0;

printf("Pi estimate using infinite series: %f
", pi_estimate);

return 0;
}
```

The above code sums the first one million terms of the Gregory-Leibniz series and multiplies the result by four to obtain an estimate of pi. The variable `sign` alternates between positive and negative values, and the sum only considers odd denominators to align with the formula shown above.

Conclusion

In conclusion, pi is a mathematical constant with a plethora of applications in different fields. Its value can be approximated with different methods, but the Monte Carlo method and infinite series are some of the most popular and versatile ones. The code examples presented in this article aim to give the reader a basic understanding of how to implement these methods in C, but it is important to remember their assumptions and limitations when applying them to real-world scenarios.

## Popular questions

1. What is the Monte Carlo method for calculating pi in C?
The Monte Carlo method involves generating random points within a unit square and counting the number of points that fall within the inscribed unit circle. The ratio of points within the circle to the total number of points generated provides an estimate of pi.

2. How do you implement the Monte Carlo method for calculating pi in C?
To implement the Monte Carlo method in C, one would need to use a loop to generate a large number of random points, check if each point falls within the unit circle, count the number of points within the circle, and then calculate the pi estimate using the ratio of points within the circle to the total number of points generated.

3. What is the infinite series method for calculating pi in C?
The infinite series method involves using mathematical formulas that converge to the value of pi after an infinite number of terms. The most famous of these formulas is the Leibniz formula, which alternates the signs of the terms and converges slowly. The Gregory-Leibniz series converges much faster and provides better results with fewer terms.

4. How do you implement the infinite series method for calculating pi in C?
To implement the infinite series method in C, one would need to define a loop that goes over a large number of terms in a particular formula, summing their values to obtain an approximation of pi. The more terms, the more accurate the estimate.

5. What are some applications of pi in C?
Pi is used in a wide range of applications, such as calculating areas and volumes of shapes, determining angular and linear measurements, and designing electrical circuits. It is also used in generating random numbers and simulating physical processes, among other things.

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##### Ajay Kemparaj
Throughout my career, I have held positions ranging from Associate Software Engineer to Principal Engineer and have excelled in high-pressure environments. My passion and enthusiasm for my work drive me to get things done efficiently and effectively. I have a balanced mindset towards software development and testing, with a focus on design and underlying technologies. My experience in software development spans all aspects, including requirements gathering, design, coding, testing, and infrastructure. I specialize in developing distributed systems, web services, high-volume web applications, and ensuring scalability and availability using Amazon Web Services (EC2, ELBs, autoscaling, SimpleDB, SNS, SQS). Currently, I am focused on honing my skills in algorithms, data structures, and fast prototyping to develop and implement proof of concepts. Additionally, I possess good knowledge of analytics and have experience in implementing SiteCatalyst. As an open-source contributor, I am dedicated to contributing to the community and staying up-to-date with the latest technologies and industry trends.
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