C Primer Plus 第9章 函数 编程练习

8.
int choice(int a,int b,int c){
int max;
max = a;
if (b > max)
max = b;
if (c > max)
max = c;
return max;
}

9.
#include <stdio.h>

void menu(void);
int choice(int low,int high);

int main(void){
menu();
int ch = choice(1,4);
switch (ch){
case 1:printf("you choice is : copy files\n");
break;
case 2:printf("you choice is : move files\n");
break;
case 3:printf("you choice is : remove files\n");
break;
case 4:break;
}
printf("Bye~");

return 0;
}

void menu(void){
printf("Please choose one of the following:\n");
printf("1) copy files        2) move files\n");
printf("3) remove files      4) quit\n");
printf("Enter the number of your choice:");
return;
}

int choice(int low,int high){
int ch;
if (scanf("%d", &ch) != 1)
return 4;
while (ch > high || ch < low){
menu();
ch = choice(1,4);
}

return ch;
}

1.
#include <stdio.h>
double min(double a, double b);

int main(void){
double x = 1.0;
double y = 2.0;
double c;
c = min(1,2);
printf("%.2f", c);
}

double min(double a, double b){
return ( b < a ? b : a);
}

2.
#include <stdio.h>
void chline(char ch, int i, int j);

int main(void){
char ch = '*';
int row = 5, col = 10;
chline(ch,row,col);
return 0;
}

void chline(char ch, int i, int j){
for (int x = 0; x < i; ++x) {
for (int y = 0; y < j; ++y) {
putchar(ch);
}
putchar('\n');
}
}

3.
#include <stdio.h>
void chline(char ch, int i, int j);

char character(void);
int number(void);
int main(void){
char ch;
int row, col;
while ((ch = character()) != 'q'){
printf("Please enter the number of lines to be printed：");
row = number();
printf("Please enter the number of columns to be printed：");
col = number();
chline(ch, row, col);
}
return 0;
}

void chline(char ch, int i, int j){
for (int x = 0; x < i; ++x) {
for (int y = 0; y < j; ++y) {
putchar(ch);
}
putchar('\n');
}
}

char character(void){
char ch;
printf("Please enter the character you need print(q to quit):");
while ((ch = getchar()) == '\n')
continue;
while (getchar() != '\n')
continue;
return ch;
}

int number(void){
int num;
char ch;
while (scanf("%d", &num) != 1){
while ((ch = getchar()) != '\n') //处理错误输出***
putchar(ch);
printf("is not an number.\n");
printf("Please enter an number such as 3,5");
}
if (num <= 0){
printf("Please enter the number than 0:");
while ((ch = getchar()) != '\n') //处理错误输出
putchar(ch);
num = number();
}
return num;
}

4.
#include <stdio.h>
double countdouwn_average(double num1, double num2);

int main(void){
double a = 10, b = 20, c;
c = countdouwn_average(a,b);
printf("%lf",c);
return 0;
}

double countdouwn_average(double num1, double num2){
double countdown1,countdown2,ctd_average;
countdown1 = 1 / num1;
countdown2 = 1 / num2;
ctd_average = 1 / ((countdown1 + countdown2) / 2);
return ctd_average;
}

5.
#include <stdio.h>
void larger_of(double * num1, double * num2);

int main(void){
double a = 10, b = 20;
larger_of(&a,&b);
printf("%.2lf  %.2lf", a, b);
return 0;
}
void larger_of(double * num1, double * num2){
double max;
max = *num1 > *num2 ? *num1 : *num2;
*num1 = max;
*num2 = max;
return;
}

6.
#include <stdio.h>
void larger_of(double * num1, double * num2, double * num3);

int main(void){
double a = 60, b = 39, c = 50;
larger_of(&a,&b,&c);
printf("%.2lf  %.2lf  %.2lf", a, b, c);
return 0;
}

void larger_of(double * num1, double * num2, double * num3){
double max,min,c;
max = * num1;
if (max < *num2)
max = *num2;
if (max < *num3)
max = *num3;
min = * num1;
if (min > *num2)
min = *num2;
if (min > *num3)
min = *num3;
c = *num1 + *num2 + *num3 - min - max;
*num1 = min;
*num2 = c;
*num3 = max;
}

7.
#include <stdio.h>
#include <ctype.h>
int show_location(char ch);

int main(void){
char ch;
printf("Please enter the charaster:");
while ((ch = getchar()) != '\n'){  //ch = getchar()要框起来。
printf("%c,%d\n", ch,show_location(ch));
}

return 0;
}
//用isaplpa 和 toupper我是真不会。看了答案
//发现答案真机智～
int show_location(char ch){
int result;
if (isalpha(ch)){
result = toupper(ch) - 'A' + 1;
} else result = -1;

return result;
}

8.
#include <stdio.h>
double power(double n, double p);

int main(void){
double a = 2,b = 2;
printf("%lf", power(a,b));
return 0;
}

double power(double n, double p){
double pow = 1;
int i;
if (n == 0)
return 0;
if (p == 0)
return 1;
if (p > 0){
for (i = 1;i <= p; i++) {
pow = pow * n;
}
return pow;
}
if (p < 0){
for (i = 1;i  <= -p ; i++) {
pow = pow * n;
}
return 1 / pow;
}
}

9.
#include <stdio.h>
double power(double n, double p);

int main(void){
double a = 2,b = -2;
printf("%lf", power(a,b));
return 0;
}

double power(double n, double p){
double pow = 1;
int i;
if (n == 0)
return 0;
if (p == 0)
return 1;
if (p > 0){
for (i = 1;i <= p; i++) {
pow = pow * n;
}
return pow;
}
if (p < 0){
return 1 / power(n, -p);
}
}

10.
#include <stdio.h>
void to_binary(int a, int b);

int main(void){
int a,b;
char ch;
printf("Please enter an integer(q to quit):");
while (scanf("%d", &a) == 1){
printf("Please enter number base (2-10):");
while (scanf("%d", &b) == 1 && b >= 2 && b <= 10){
to_binary(a,b);
putchar('\n');
break;
}
while ((ch = getchar()) != '\n'); //处理错误输入
printf("Please enter an integer(q to quit):");
}
return 0;
}

void to_binary(int a, int b){
int r;
r = a % b;
if (a > b)
to_binary(a / b, b);
printf("%d", r); //暂时不理解putchar('0' + r)是什么意思，所以就先用这个吧。
return;
}