/*
    bisec2_2.c: 初期区間逆入力可能バージョン
 */
#include <stdio.h>
#include <math.h>
#define N 100

double f(double x)
//  f(x) = x^2 - 2
{
    return x * x - 2.0;
}

int main(void)
{
    int n=0;
    double x1=1, x2=2, x3, err;
    double eps = 1.0e-6;
    char s[128];

    fprintf(stderr, "# x1, x2 = "); fgets(s, 128, stdin);
    sscanf(s, "%lf%lf", &x1, &x2);
    fprintf(stderr, "# eps = "); fgets(s, 128, stdin);
    sscanf(s, "%lf", &eps);
    printf("# n, x, err\n");
    do {
        n++;
        if (n > N) {
            fprintf(stderr, "*** 反復回数が100回を超えました。***");
            break;
        }
        x3 = (x1 + x2) / 2.0;
        if (f(x1)*f(x3) < 0.0) x2 = x3;
        else                   x1 = x3;
        err = fabs(x2 - x1);
        printf("%4d, % .15e, % .15e\n", n, x3, err);
    } while (err >= eps);
    printf("\n# sqrt(2) = % .15e\n", (x1 + x2) / 2.0);
    return 0;
}
/*  ---   実行例   ---
Z:\proen1\kadai4>bisec2_2
# x1, x2 = 2 1
# eps = 1e-6
# n, x, err
   1,  1.500000000000000e+000,  5.000000000000000e-001
   2,  1.250000000000000e+000,  2.500000000000000e-001
   3,  1.375000000000000e+000,  1.250000000000000e-001
   4,  1.437500000000000e+000,  6.250000000000000e-002
   5,  1.406250000000000e+000,  3.125000000000000e-002
   6,  1.421875000000000e+000,  1.562500000000000e-002
   7,  1.414062500000000e+000,  7.812500000000000e-003
   8,  1.417968750000000e+000,  3.906250000000000e-003
   9,  1.416015625000000e+000,  1.953125000000000e-003
  10,  1.415039062500000e+000,  9.765625000000000e-004
  11,  1.414550781250000e+000,  4.882812500000000e-004
  12,  1.414306640625000e+000,  2.441406250000000e-004
  13,  1.414184570312500e+000,  1.220703125000000e-004
  14,  1.414245605468750e+000,  6.103515625000000e-005
  15,  1.414215087890625e+000,  3.051757812500000e-005
  16,  1.414199829101563e+000,  1.525878906250000e-005
  17,  1.414207458496094e+000,  7.629394531250000e-006
  18,  1.414211273193359e+000,  3.814697265625000e-006
  19,  1.414213180541992e+000,  1.907348632812500e-006
  20,  1.414214134216309e+000,  9.536743164062500e-007

# sqrt(2) =  1.414213657379150e+000
*/