学完C语言之后，我就去阅读《C Primer Plus》这本经典的C语言书籍，对每一章的编程练习题都做了相关的解答，仅仅代表着我个人的解答思路，如有错误，请各位大佬帮忙点出！

1.设计一个函数min(x, y)，返回两个double类型值的较小值。在一个简单 的驱动程序中测试该函数。

#include <stdio.h>
double Min(double x, double y)
{return x > y ? y : x;
}
int main(void)
{double min_num = Min(20.0, 15.0);printf("min_num : %lf\n", min_num);min_num = Min(15.0, 20.0);printf("min_num : %lf\n", min_num);return 0;
}

2.设计一个函数chline(ch, i, j)，打印指定的字符j行i列。在一个简单的驱 动程序中测试该函数。

#include <stdio.h>
void chline(char ch, int i, int j)
{for (int m = 0; m < i; m++){for (int n = 0; n < j; n++){printf("%c ", ch);}printf("\n");}
}
int main(void)
{char ch = '0';int i = 0, j = 0;printf("请输入一个字符:");scanf("%c",&ch);printf("请输入行数:");scanf("%d", &i);printf("请输入列数:");scanf("%d", &j);chline(ch, i, j);return 0;
}

3.编写一个函数，接受3个参数：一个字符和两个整数。字符参数是待 打印的字符，第1个整数指定一行中打印字符的次数，第2个整数指定打印指 定字符的行数。编写一个调用该函数的程序。

#include <stdio.h>
void chline(char ch, int i, int j)
{for (int m = 0; m < j; m++){for (int n = 0; n < i; n++){printf("%c ", ch);}printf("\n");}
}
int main(void)
{char ch = '0';int i = 0, j = 0;printf("请输入一个字符:");scanf("%c",&ch);printf("请输入一行中打印字符的个数:");scanf("%d", &i);printf("请输入指定打印字符的个数:");scanf("%d", &j);chline(ch, i, j);return 0;
}

4.两数的调和平均数这样计算：先得到两数的倒数，然后计算两个倒数 的平均值，最后取计算结果的倒数。编写一个函数，接受两个double类型的 参数，返回这两个参数的调和平均数。

#include <stdio.h>
double Reconcile_the_average(double d1, double d2)
{return 1.0 / ((1.0 / d1 + 1.0 / d2) / 2.0);
}
int main(void)
{double ret = Reconcile_the_average(3.0,4.0);printf("ret : %lf\n", ret);ret = Reconcile_the_average(4.0, 5.0);printf("ret : %lf\n", ret);return 0;
}

5.编写并测试一个函数larger_of()，该函数把两个double类型变量的值替 换为较大的值。例如， larger_of(x, y)会把x和y中较大的值重新赋给两个变 量。

#include <stdio.h>
void larger_of(double* d1,double* d2)
{if (*d1 > *d2)*d2 = *d1;else*d1 = *d2;
}
int main(void)
{double d1 = 1.0, d2 = 2.0, d3 = 3.0,d4 = 4.0;printf("d1 = %lf,d2 = %lf d3 = %lf,d4 = %lf\n", d1, d2, d3, d4);larger_of(&d1, &d2);larger_of(&d3, &d4);printf("d1 = %lf,d2 = %lf d3 = %lf,d4 = %lf\n", d1, d2, d3, d4);return 0;
}

6.编写并测试一个函数，该函数以3个double变量的地址作为参数，把最 小值放入第1个函数，中间值放入第2个变量，最大值放入第3个变量。

#include <stdio.h>
void sort(double* d1, double* d2, double* d3)
{double temp = 0.0;if (*d1 > *d2){temp = *d1;*d1 = *d2;*d2 = temp;}if (*d1 > *d3){temp = *d1;*d1 = *d3;*d3 = temp;}if (*d2 > *d3){temp = *d2;*d2 = *d3;*d3 = temp;}
}
int main(void)
{double d1 = 2.0, d2 = 3.0, d3 = 1.0;printf("排序前:d1 = %lf,d2 = %lf,d3 = %lf\n", d1, d2, d3);sort(&d1, &d2, &d3);printf("排序后:d1 = %lf,d2 = %lf,d3 = %lf\n", d1, d2, d3);return 0;
}

7.编写一个函数，从标准输入中读取字符，直到遇到文件结尾。程序要 报告每个字符是否是字母。如果是，还要报告该字母在字母表中的数值位 置。例如，c和C在字母表中的位置都是3。合并一个函数，以一个字符作为 参数，如果该字符是一个字母则返回一个数值位置，否则返回-1。

#include <stdio.h>
#include <ctype.h>
int position(char ch)
{if (islower(ch))return ch - 'a' + 1;else if (isupper(ch))return ch - 'A' + 1;return -1;
}
void get_char_pos(void)
{char ch = '0';printf("请输入一些字符:");while ((ch = getchar()) != EOF){if (ch == '\n')continue;if (position(ch) != -1)printf("该字符是一个字母，且位于字母表第%d位\n", position(ch));else{printf("该字符不是一个字母\n");}}
}
int main(void)
{get_char_pos();return 0;
}

8.第6章的程序清单6.20中，power()函数返回一个double类型数的正整数 次幂。改进该函数，使其能正确计算负幂。另外，函数要处理0的任何次幂 都为0，任何数的0次幂都为1（函数应报告0的0次幂未定义，因此把该值处 理为1）。要使用一个循环，并在程序中测试该函数。

#include <stdio.h>
double power(double n, int p)
{int i;double pow = 1.0;if ((0 == p) && (0 == n)){printf("0 to the 0 undefined, using 1 as the value.\n");return pow;}if (0 == n){pow = 0.0;return pow;}if (0 == p){return pow;}if (p > 0){for (i = 1; i <= p; i++){pow *= n;}return pow;}else{for (i = 1; i <= -p; i++){pow *= 1 / n;}return pow;}
}
int main(void)
{double x, xpow;int exp;printf("Enter a number and the integer power");printf(" to which\nthe number will be raised. Enter q");printf(" to quit.\n");while (scanf("%lf%d", &x, &exp) == 2){xpow = power(x, exp);printf("%.3g to the power %d is %.5g.\n", x, exp, xpow);printf("Enter next pair of numbers or q to quit.\n");}printf("Hope you enjoyed this power trip -- bye!\n");return 0;
}

9.使用递归函数重写编程练习8。

#include <stdio.h>
double power(double n, int p)
{double pow = 1.0;if ((0 == p) && (0 == n)){printf("0 to the 0 undefined, using 1 as the value.\n");return pow;}if (0 == n){pow = 0.0;return pow;}if (0 == p){return pow;}if (p > 0){return n * power(n, p - 1);}else{return power(n, p + 1) / n;}
}
int main(void)
{double x, xpow;int exp;printf("Enter a number and the integer power");printf(" to which\nthe number will be raised. Enter q");printf(" to quit.\n");while (scanf("%lf %d", &x, &exp) == 2){xpow = power(x, exp);printf("%.3g to the power %d is %.5g.\n", x, exp, xpow);printf("Enter next pair of numbers or q to quit.\n");}printf("Hope you enjoyed this power trip -- bye!\n");return 0;
}

10.为了让程序清单9.8中的to_binary()函数更通用，编写一个to_base_n() 函数接受两个在2～10范围内的参数，然后以第2个参数中指定的进制打印第 1个参数的数值。例如，to_base_n(129， 8)显示的结果为201，也就是129的 八进制数。在一个完整的程序中测试该函数。

#include <stdio.h>
void to_base_n(int x, int base)
{int r;r = x % base;if (x >= base){to_base_n(x / base, base);}printf("%d", r);return;
}
int main(void)
{int b;long int n;printf("Please enter a number (q to quit): ");while (scanf("%ld", &n) == 1){if (n <= 0){printf("Illegal data! Please enter again: ");continue;}printf("Please enter a base system number (2 - 10): ");while (scanf("%d", &b) != 1 || (b < 2 || b > 10)){while (getchar() != '\n')continue;printf("Please enteragain (2 - 10): ");}printf("%d in %d base system is: ", n, b);to_base_n(n, b);printf("\nYou can enter a number again (q to quit): ");}printf("Done.\n");return 0;
}

11.编写并测试Fibonacci()函数，该函数用循环代替递归计算斐波那契 数。

#include <stdio.h>
void Fibonacci(int len)
{int i;unsigned long t, x, y;x = y = 1;for (i = 0; i < len; i++){printf("%lu\n", x);t = x + y;x = y;y = t;}return;
}
int main(void)
{int n;printf("Please enter a integer (<= 0 or q to quit): ");while (scanf("%d", &n) == 1){printf("Top %d items of Fibonacci sequence:\n", n);Fibonacci(n);printf("You can enter again (<= 0 or q to quit): ");}printf("Done.\n");return 0;
}