今日のCの警告 warning: type specifier missing, defaults to 'int'

計算物理学 Rubin H. Landau 参考文献・docker登録
https://qiita.com/kaizen_nagoya/items/af924f5ac71ff5cc8c89

docker/ubuntu

# cd /home/cp/HCPcodes
# clang pond.c -o pond
pond.c:19:1: warning: type specifier missing, defaults to 'int' [-Wimplicit-int]
main()  {
^
1 warning generated.
# ./pond
data stored in pond.dat
# cat pond.dat
1	4.000000
2	4.000000
...
998	3.130261
999	3.131131
1000	3.132000
# gcc pond.c
pond.c:19:1: warning: return type defaults to ‘int’ [-Wimplicit-int]
 main()  {
 ^~~~

main関数の前にint をつければよい。

vond.c

/* From "COMPUTATIONAL PHYSICS", 3rd Ed, Enlarged Python eTextBook  
    by RH Landau, MJ Paez, and CC Bordeianu
    Copyright Wiley-VCH Verlag GmbH & Co. KGaA, Berlin;  Copyright R Landau,
    Oregon State Unv, MJ Paez, Univ Antioquia, C Bordeianu, Univ Bucharest, 2015.
    Support by National Science Foundation
*/
//https://physics.oregonstate.edu/~landaur/Books/CPbook/Codes/HPCodes/pond.c
// pond.c: *Monte-Carlo integration to determine pi (stone throwing 

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

// if you don't have drand48 uncomment the following two lines 
//    #define drand48 1.0/RAND_MAX*rand 
//    #define srand48 srand              

#define max 1000                     // number of stones to be thrown
#define seed 68111                       // seed for number generator

int main()  {
	
  int i, pi = 0;
  double x, y, area;
  FILE *output;                              // save data in pond.dat
  output = fopen("pond.dat","w");
  srand48(seed);                         // seed the number generator
  for (i = 1; i<= max; i++) {
    x = drand48()*2-1;                      // creates floats between
    y = drand48()*2-1;                                    // 1 and -1
    if ((x*x + y*y)<1) pi++;                    // stone hit the pond
    area = 4*(double)pi/i;                          // calculate area
    fprintf(output, "%i\t%f\n", i, area);
  }
  printf("data stored in pond.dat\n");
  fclose(output);
  return i;
}

＜この記事は個人の過去の経験に基づく個人の感想です。現在所属する組織、業務とは関係がありません。＞
This article is an individual impression based on the individual's experience. It has nothing to do with the organization or business to which I currently belong.

文書履歴(document history)

ver. 0.01 初稿 20190818
ver. 0.04 URL追記　20230302

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