一直線上にない3点 A,B,C が作る角度の大きさ（鋭角、直角、鈍角）


#include <stdio.h>

#include <stdlib.h>

#include <time.h>

#include <math.h>



typedef struct POINT { float x, y; } POINT;



const char *GetTheStringOfIndicatesTheAngleAttribute( POINT A, POINT B, POINT C ){

    static const char *S[] = {"an acute angle","a right angle","an obtuse angle"};

    int    attribute = (A.x-B.x)*(C.x-B.x) + (A.y-B.y)*(C.y-B.y);

    return 0<attribute ? S[0] : ( attribute<0 ? S[2] : S[1] );

}



double GetTheAngleAsDegree( POINT A, POINT B, POINT C ){

    double d = (A.x-B.x)*(C.x-B.x) + (A.y-B.y)*(C.y-B.y);

    double m = sqrt( (A.x-B.x)*(A.x-B.x) + (A.y-B.y)*(A.y-B.y) )

             * sqrt( (C.x-B.x)*(C.x-B.x) + (C.y-B.y)*(C.y-B.y) );

    return (180./3.14159265358979323846)*acos(d/m); //cos: transcendental functions

}




int main(){ srand((unsigned int)time(NULL));
     for(int e=0; e<64; e++ ) { // 0
<= x < 1000, 0 <= y < 1000

        POINT A = (POINT){ rand() % 1000, rand() % 1000 };

        POINT B = (POINT){ rand() % 1000, rand() % 1000 };

        POINT C = (POINT){ rand() % 1000, rand() % 1000 };

        if( (A.x-C.x)*(B.y-C.y) == (B.x-C.x)*(A.y-C.y) ) continue;



        printf( "A:(% 5.0f,% 5.0f), ", A.x, A.y );

        printf( "B:(% 5.0f,% 5.0f), ", B.x, B.y );

        printf( "C:(% 5.0f,% 5.0f)\n", C.x, C.y );


        double AngleABC = GetTheAngleAsDegree( A, B, C );

        double AngleBCA = GetTheAngleAsDegree( B, C, A );

        double AngleCAB = GetTheAngleAsDegree( C, A, B );


        const char *abc = GetTheStringOfIndicatesTheAngleAttribute( A, B, C );

        const char *bca = GetTheStringOfIndicatesTheAngleAttribute( B, C, A );

        const char *cab = GetTheStringOfIndicatesTheAngleAttribute( C, A, B );



        printf("\t Angle ABC, %6.2f deg., is %s.\n", AngleABC, abc );

        printf("\t Angle BCA, %6.2f deg., is %s.\n", AngleBCA, bca );

        printf("\t Angle CAB, %6.2f deg., is %s.\n", AngleCAB, cab );


        printf( "\n");

    }

    return 0;

}

・インライン展開でも支障ない程の、簡単な四則演算のみの短くシンプルな実装
・rand() 関数を使って、点Ａ,Ｂ,Ｃの座標を動的に作成した検証用データ
・３点が一直線上にあるかの判定処理（一直線上にある時、角度は常に０°になってしまう）
　　　　　　if( (A.x-C.x)*(B.y-C.y)==(B.x-C.x)*(A.y-C.y) )continue;

実行結果　『 ∠ABC、∠BCA 、∠CAB を調べた結果を表示』

A:(   27,  565), B:(    7,  807), C:(   75,  349)
         Angle ABC,   3.72 deg., is an acute angle.
         Angle BCA,   4.08 deg., is an acute angle.
         Angle CAB, 172.20 deg., is an obtuse angle.

A:(  889,   21), B:(  709,  122), C:(  795,  624)
         Angle ABC, 109.58 deg., is an obtuse angle.
         Angle BCA,  18.58 deg., is an acute angle.
         Angle CAB,  51.84 deg., is an acute angle.

A:(   66,  317), B:(  902,  839), C:(  299,   82)
         Angle ABC,  19.48 deg., is an acute angle.
         Angle BCA,  83.29 deg., is an acute angle.
         Angle CAB,  77.23 deg., is an acute angle.

A:(  948,   48), B:(  846,   21), C:(  960,  252)
         Angle ABC,  48.91 deg., is an acute angle.
         Angle BCA,  22.90 deg., is an acute angle.
         Angle CAB, 108.19 deg., is an obtuse angle.

A:(  938,  783), B:(  216,   40), C:(  742,   25)
         Angle ABC,  47.45 deg., is an acute angle.
         Angle BCA, 102.86 deg., is an obtuse angle.
         Angle CAB,  29.68 deg., is an acute angle.

A:(  194,  934), B:(  703,   16), C:(  413,  163)
         Angle ABC,  34.11 deg., is an acute angle.
         Angle BCA, 132.74 deg., is an obtuse angle.
         Angle CAB,  13.15 deg., is an acute angle.

A:(  817,  626), B:(  705,   50), C:(  753,  728)
         Angle ABC,   6.95 deg., is an acute angle.
         Angle BCA,  36.16 deg., is an acute angle.
         Angle CAB, 136.89 deg., is an obtuse angle.

A:(  658,    1), B:(  184,  924), C:(  905,  411)
         Angle ABC,  27.39 deg., is an acute angle.
         Angle BCA,  94.37 deg., is an obtuse angle.
         Angle CAB,  58.25 deg., is an acute angle.

A:(  338,  836), B:(   35,  118), C:(  559,  368)
         Angle ABC,  41.61 deg., is an acute angle.
         Angle BCA,  90.23 deg., is an obtuse angle.
         Angle CAB,  48.16 deg., is an acute angle.

A:(  166,  861), B:(  682,  593), C:(  642,  896)
         Angle ABC,  55.03 deg., is an acute angle.
         Angle BCA,  93.31 deg., is an obtuse angle.
         Angle CAB,  31.65 deg., is an acute angle.

A:(  617,  482), B:(   52,   18), C:(  876,  660)
         Angle ABC,   1.47 deg., is an acute angle.
         Angle BCA,   3.42 deg., is an acute angle.
         Angle CAB, 175.10 deg., is an obtuse angle.

A:(  129,  228), B:(   49,  372), C:(  624,  785)
         Angle ABC,  96.63 deg., is an obtuse angle.
         Angle BCA,  12.68 deg., is an acute angle.
         Angle CAB,  70.68 deg., is an acute angle.

A:(  646,  591), B:(  104,  242), C:(  721,  410)
         Angle ABC,  17.55 deg., is an acute angle.
         Angle BCA,  82.72 deg., is an acute angle.
         Angle CAB,  79.73 deg., is an acute angle.

A:(  861,  722), B:(   53,  803), C:(  781,  180)
         Angle ABC,  34.83 deg., is an acute angle.
         Angle BCA,  57.84 deg., is an acute angle.
         Angle CAB,  87.33 deg., is an acute angle.

A:(  926,  628), B:(  696,  148), C:(  679,  385)
         Angle ABC,  29.70 deg., is an acute angle.
         Angle BCA, 130.43 deg., is an obtuse angle.
         Angle CAB,  19.87 deg., is an acute angle.

A:(  191,  627), B:(  658,  903), C:(  556,   95)
         Angle ABC,  52.22 deg., is an acute angle.
         Angle BCA,  41.65 deg., is an acute angle.
         Angle CAB,  86.13 deg., is an acute angle.

A:(  376,  424), B:(   27,  970), C:(  129,    4)
         Angle ABC,  26.56 deg., is an acute angle.
         Angle BCA,  36.49 deg., is an acute angle.
         Angle CAB, 116.95 deg., is an obtuse angle.

A:(  127,  514), B:(  326,  938), C:(  119,  425)
         Angle ABC,   3.17 deg., is an acute angle.
         Angle BCA,  16.84 deg., is an acute angle.
         Angle CAB, 159.99 deg., is an obtuse angle.

A:(  933,  431), B:(  154,  118), C:(  372,  766)
         Angle ABC,  49.52 deg., is an acute angle.
         Angle BCA,  77.75 deg., is an acute angle.
         Angle CAB,  52.73 deg., is an acute angle.

A:(  866,  620), B:(  522,  962), C:(  493,  705)
         Angle ABC,  51.61 deg., is an acute angle.
         Angle BCA,  96.40 deg., is an obtuse angle.
         Angle CAB,  32.00 deg., is an acute angle.

A:(  507,  856), B:(  737,  809), C:(  258,  376)
         Angle ABC,  53.66 deg., is an acute angle.
         Angle BCA,  20.47 deg., is an acute angle.
         Angle CAB, 105.87 deg., is an obtuse angle.

A:(  169,  268), B:(  692,  644), C:(  363,  422)
         Angle ABC,   1.70 deg., is an acute angle.
         Angle BCA, 175.57 deg., is an obtuse angle.
         Angle CAB,   2.73 deg., is an acute angle.

A:(  386,  962), B:(  389,  205), C:(  543,  935)
         Angle ABC,  12.14 deg., is an acute angle.
         Angle BCA,  87.85 deg., is an acute angle.
         Angle CAB,  80.01 deg., is an acute angle.

A:(  695,  928), B:(  579,  741), C:(  561,  158)
         Angle ABC, 149.96 deg., is an obtuse angle.
         Angle BCA,   8.10 deg., is an acute angle.
         Angle CAB,  21.94 deg., is an acute angle.

A:(  271,  614), B:(   48,  117), C:(  426,  785)
         Angle ABC,   5.34 deg., is an acute angle.
         Angle BCA,  12.69 deg., is an acute angle.
         Angle CAB, 161.98 deg., is an obtuse angle.

A:(  430,  644), B:(   92,  109), C:(  696,  387)
         Angle ABC,  33.00 deg., is an acute angle.
         Angle BCA,  68.73 deg., is an acute angle.
         Angle CAB,  78.27 deg., is an acute angle.

A:(    9,  708), B:(  748,  321), C:(  128,  762)
         Angle ABC,   7.78 deg., is an acute angle.
         Angle BCA, 120.17 deg., is an obtuse angle.
         Angle CAB,  52.05 deg., is an acute angle.

A:(  402,  446), B:(  420,  173), C:(  978,   42)
         Angle ABC, 106.98 deg., is an obtuse angle.
         Angle BCA,  21.83 deg., is an acute angle.
         Angle CAB,  51.18 deg., is an acute angle.

A:(  170,  623), B:(  902,  494), C:(  620,   41)
         Angle ABC,  68.09 deg., is an acute angle.
         Angle BCA,  69.61 deg., is an acute angle.
         Angle CAB,  42.29 deg., is an acute angle.

A:(  322,  850), B:(  918,  875), C:(   97,  486)
         Angle ABC,  22.95 deg., is an acute angle.
         Angle BCA,  32.93 deg., is an acute angle.
         Angle CAB, 124.12 deg., is an obtuse angle.

A:(  223,   74), B:(  305,  989), C:(  787,  353)
         Angle ABC,  42.28 deg., is an acute angle.
         Angle BCA,  79.16 deg., is an acute angle.
         Angle CAB,  58.56 deg., is an acute angle.

A:(   27,  671), B:(  542,  803), C:(  148,  486)
         Angle ABC,  24.44 deg., is an acute angle.
         Angle BCA,  84.37 deg., is an acute angle.
         Angle CAB,  71.19 deg., is an acute angle.

A:(  107,  159), B:(  719,  739), C:(  262,  125)
         Angle ABC,   9.88 deg., is an acute angle.
         Angle BCA, 114.29 deg., is an obtuse angle.
         Angle CAB,  55.83 deg., is an acute angle.

A:(  158,  658), B:(  735,  681), C:(  126,  699)
         Angle ABC,   3.98 deg., is an acute angle.
         Angle BCA,  50.34 deg., is an acute angle.
         Angle CAB, 125.69 deg., is an obtuse angle.

A:(  288,  366), B:(  299,  954), C:(  528,  252)
         Angle ABC,  19.14 deg., is an acute angle.
         Angle BCA,  46.53 deg., is an acute angle.
         Angle CAB, 114.34 deg., is an obtuse angle.

A:(  396,   73), B:(  465,  828), C:(  849,  749)
         Angle ABC,  83.60 deg., is an acute angle.
         Angle BCA,  67.80 deg., is an acute angle.
         Angle CAB,  28.60 deg., is an acute angle.

A:(  991,  739), B:(    2,  734), C:(  923,   54)
         Angle ABC,  36.73 deg., is an acute angle.
         Angle BCA,  59.23 deg., is an acute angle.
         Angle CAB,  84.04 deg., is an acute angle.

A:(   81,  747), B:(  710,  630), C:(  434,  365)
         Angle ABC,  54.37 deg., is an acute angle.
         Angle BCA,  88.91 deg., is an acute angle.
         Angle CAB,  36.72 deg., is an acute angle.

A:(  522,  564), B:(  122,  435), C:(  581,  430)
         Angle ABC,  18.50 deg., is an acute angle.
         Angle BCA,  65.61 deg., is an acute angle.
         Angle CAB,  95.89 deg., is an obtuse angle.

A:(  526,  951), B:(  551,  234), C:(  358,  374)
         Angle ABC,  52.05 deg., is an acute angle.
         Angle BCA, 109.72 deg., is an obtuse angle.
         Angle CAB,  18.23 deg., is an acute angle.

A:(  743,  858), B:(  106,  589), C:(  744,  536)
         Angle ABC,  27.64 deg., is an acute angle.
         Angle BCA,  85.07 deg., is an acute angle.
         Angle CAB,  67.28 deg., is an acute angle.

A:(  483,  378), B:(  298,   60), C:(  205,  553)
         Angle ABC,  40.87 deg., is an acute angle.
         Angle BCA,  47.13 deg., is an acute angle.
         Angle CAB,  92.00 deg., is an obtuse angle.

A:(   22,  645), B:(  723,    0), C:(  602,  301)
         Angle ABC,  25.48 deg., is an acute angle.
         Angle BCA, 142.57 deg., is an obtuse angle.
         Angle CAB,  11.95 deg., is an acute angle.

A:(  748,  453), B:(  470,  256), C:(  757,  670)
         Angle ABC,  19.95 deg., is an acute angle.
         Angle BCA,  32.36 deg., is an acute angle.
         Angle CAB, 127.70 deg., is an obtuse angle.

A:(  942,  133), B:(  343,  722), C:(  881,  957)
         Angle ABC,  68.11 deg., is an acute angle.
         Angle BCA,  70.64 deg., is an acute angle.
         Angle CAB,  41.25 deg., is an acute angle.

A:(  522,  766), B:(   17,  908), C:(  162,  346)
         Angle ABC,  59.83 deg., is an acute angle.
         Angle BCA,  55.07 deg., is an acute angle.
         Angle CAB,  65.10 deg., is an acute angle.

A:(   84,  246), B:(  257,  549), C:(  578,  748)
         Angle ABC, 151.52 deg., is an obtuse angle.
         Angle BCA,  13.66 deg., is an acute angle.
         Angle CAB,  14.82 deg., is an acute angle.

A:(  533,  398), B:(  376,  247), C:(  947,  661)
         Angle ABC,   7.94 deg., is an acute angle.
         Angle BCA,   3.52 deg., is an acute angle.
         Angle CAB, 168.54 deg., is an obtuse angle.

A:(  565,  780), B:(  404,  193), C:(  651,  761)
         Angle ABC,   8.16 deg., is an acute angle.
         Angle BCA,  78.96 deg., is an acute angle.
         Angle CAB,  92.88 deg., is an obtuse angle.

A:(  343,  644), B:(  168,  159), C:(  360,  620)
         Angle ABC,   2.77 deg., is an acute angle.
         Angle BCA, 122.08 deg., is an obtuse angle.
         Angle CAB,  55.15 deg., is an acute angle.

A:(  717,  640), B:(  439,  770), C:(  231,  795)
         Angle ABC, 161.79 deg., is an obtuse angle.
         Angle BCA,  10.84 deg., is an acute angle.
         Angle CAB,   7.37 deg., is an acute angle.

A:(  116,  720), B:(  780,  261), C:(  986,  919)
         Angle ABC,  72.73 deg., is an acute angle.
         Angle BCA,  59.73 deg., is an acute angle.
         Angle CAB,  47.54 deg., is an acute angle.

A:(  896,  642), B:(  657,  143), C:(  865,   93)
         Angle ABC,  77.92 deg., is an acute angle.
         Angle BCA,  79.72 deg., is an acute angle.
         Angle CAB,  22.36 deg., is an acute angle.

A:(  248,  290), B:(  271,  244), C:(  690,  379)
         Angle ABC,  98.71 deg., is an obtuse angle.
         Angle BCA,   6.47 deg., is an acute angle.
         Angle CAB,  74.82 deg., is an acute angle.

A:(  881,  128), B:(  625,  619), C:(  500,  283)
         Angle ABC,  47.94 deg., is an acute angle.
         Angle BCA,  91.73 deg., is an obtuse angle.
         Angle CAB,  40.33 deg., is an acute angle.

A:(  673,  781), B:(  237,  875), C:(  758,  939)
         Angle ABC,  19.17 deg., is an acute angle.
         Angle BCA,  54.72 deg., is an acute angle.
         Angle CAB, 106.11 deg., is an obtuse angle.

A:(  312,  318), B:(  528,  687), C:(  866,  910)
         Angle ABC, 153.76 deg., is an obtuse angle.
         Angle BCA,  13.48 deg., is an acute angle.
         Angle CAB,  12.76 deg., is an acute angle.

A:(  574,   54), B:(  132,  455), C:(  329,  490)
         Angle ABC,  52.29 deg., is an acute angle.
         Angle BCA, 109.26 deg., is an obtuse angle.
         Angle CAB,  18.45 deg., is an acute angle.

A:(  265,  438), B:(  123,  968), C:(  978,  813)
         Angle ABC,  64.73 deg., is an acute angle.
         Angle BCA,  38.02 deg., is an acute angle.
         Angle CAB,  77.26 deg., is an acute angle.

A:(  207,  938), B:(  175,  964), C:(  274,    5)
         Angle ABC,  45.01 deg., is an acute angle.
         Angle BCA,   1.79 deg., is an acute angle.
         Angle CAB, 133.20 deg., is an obtuse angle.

A:(  994,  458), B:(  922,  245), C:(  655,  277)
         Angle ABC, 101.84 deg., is an obtuse angle.
         Angle BCA,  34.93 deg., is an acute angle.
         Angle CAB,  43.22 deg., is an acute angle.

A:(  286,  575), B:(  382,  150), C:(  271,  519)
         Angle ABC,   4.01 deg., is an acute angle.
         Angle BCA, 148.26 deg., is an obtuse angle.
         Angle CAB,  27.72 deg., is an acute angle.

A:(  644,  544), B:(  926,  508), C:(  590,   74)
         Angle ABC,  59.53 deg., is an acute angle.
         Angle BCA,  31.19 deg., is an acute angle.
         Angle CAB,  89.28 deg., is an acute angle.

A:(  614,  513), B:(  623,   27), C:(  690,  685)
         Angle ABC,   6.87 deg., is an acute angle.
         Angle BCA,  18.02 deg., is an acute angle.
         Angle CAB, 155.10 deg., is an obtuse angle.

一直線上にない3点 A,B,C が作る角度の大きさ
（鋭角、直角、鈍角）

０、はじめに

１、Ｃ言語(C99)での実装

２、テスト結果

実行結果　『 ∠ABC、∠BCA 、∠CAB を調べた結果を表示』

３、ライセンスと例外規定及び免責事項

４、終わりに

目次
	０、はじめに１、Ｃ言語(C99)での実装２、テスト結果３、ライセンス及び免責事項４、終わりに

一直線上にない3点 A,B,C が作る角度の大きさ（鋭角、直角、鈍角）

０、はじめに

１、Ｃ言語(C99)での実装

２、テスト結果

実行結果 『 ∠ABC、∠BCA 、∠CAB を調べた結果を表示 』

３、ライセンスと例外規定及び免責事項

４、終わりに

一直線上にない3点 A,B,C が作る角度の大きさ
（鋭角、直角、鈍角）

実行結果　『 ∠ABC、∠BCA 、∠CAB を調べた結果を表示』