c - 如何在C中获得最大的小数精度

Question

我在程序中使用不定的一系列项来计算 Pi。当我显示计算结果时，Pi 的整体精度不是我想要的。我相信我正在使用的转换规范或原始类型存在问题。

这是我得到的:

圆周率:3.141594

这是我想要的:

圆周率:3.14159265358979323846

这是我的 Pi 计算方法中的一些代码:

 //Global variables

 // Variables to hold the number of threads and the number of terms 
 long numOfThreads, numOfTerms;
 // Variable to store the pieces of Pi as it is being calculated by each thread
 double piTotal = 0.0;





// Use an indefinite series of terms to calulate Pi   
 void calculatePi(){
      // Variable to store the sign of each term
      double signOfTerm = 0.0;
      // Variable to to be the index of the loop variable
      long k;
 #pragma omp parallel for num_threads(numOfThreads) \
 default(none) reduction(+: piTotal) private(k, signOfTerm)\
 shared(numOfTerms)

     for (k = 0; k <= numOfTerms; k++) {
        if (k == 0) {
        signOfTerm = 1.0;
        }
     // Sign of term is even
        else if (k % 2 == 0) {
        signOfTerm = 1.0;
        }
    // Sign of term is odd
        else if (k % 2 == 1) {
        signOfTerm = -1.0;
      }
    // Computing pi using an indefinite series of terms
        piTotal += (signOfTerm) * 4 / (2 * k + 1);
        }
      }

  // Print the result
 void printResult(){
      printf("\n" "Calulation of Pi using %d " "terms: %f",numOfTerms,piTotal);
      }                              

Answer 1

这是我为解决问题所做的事情。我必须将转换规范从 %f 更改为 %.17g。这给了我比 float 的默认打印值更高的精度。

 // Print the result
 void printResult(){
      //Returning the result up to 17 places after the decimal removing trailing zeros 
      printf("\n" "The value of Pi using %d term(s): %.17g", numOfTerms, piTotal);
      }