/* 2nd_eq.c
Function: 虚数解まで広げて2次方程式の解を求める
Author: Ken
Date: 02/07/12
URL: http://blue.ribbon.to/~kenweb/
mail: kenweb@s8.xrea.com
*/
#include <stdio.h>
#include <math.h>
double calc_a_b_c(float a,float b,float c);
int main(int argc, char *argv[])
{
float a,b,c; /*変数宣言*/
fprintf(stdout,"2次方程式の解の計算\n\n"); /*方程式の係数入力*/
fprintf(stdout,"ax^2 + bx + c = 0\n\n");
fprintf(stdout,"aの値を入力してください\n");
fscanf(stdin,"%f",&a);
fprintf(stdout,"bの値を入力してください\n");
fscanf(stdin,"%f",&b);
fprintf(stdout,"cの値を入力してください\n");
fscanf(stdin,"%f",&c);
calc_a_b_c(a,b,c);
}
double calc_a_b_c(float a,float b,float c) /*解の計算*/
{
double r,l,x1,x2,x,d;
if (a==0) /*一次方程式になった場合*/
{
x=-c/b;
fprintf(stdout,"%fx + %f = 0\n",b,c);
fprintf(stdout,"x=%f\n\n",x);
return(0);
}
fprintf(stdout,"%fx^2 + %fx + %f = 0\n",a,b,c);
d=pow((double)b,2.0)-4*a*c; /*解の判別式*/
if (d<0) /*虚数解を持つとき*/
{
fprintf(stdout,"異なる2つの虚数解を持つ ( i^2 = -1 )\n");
d=-d;
r=-b/(2*a);
l=sqrt((double)d)/(2.0*a);
fprintf(stdout,"x1 = %f ",r);
if (l>=0) fprintf(stdout,"+%f i\n",l);
else fprintf(stdout,"%f i\n",l);
fprintf(stdout,"x2 = %f ",r);
if (l>=0) fprintf(stdout,"-%f i\n",l);
else fprintf(stdout,"+%f i\n",-l);
}
else if (d==0) /*重解を持つとき*/
{
x=-b/(2*a);
fprintf(stdout,"x = %f（重解）\n\n",x);
}
else if (d>0) /*２つの実数解を持つとき*/
{
x1=(-b+sqrt((double)d))/(2.0*a);
x2=(-b-sqrt((double)d))/(2.0*a);
fprintf(stdout,"異なる2つの実数解を持つ\n");
fprintf(stdout,"x1 = %f\n",x1);
fprintf(stdout,"x2 = %f\n\n",x2);
}
return(0);
}