《明解C语言》第三版 （入门篇） 第十一章练习答案

练习11-1

#include <stdio.h>
 
int main(void)
{
    char* p = "123";
 
    printf("p = \"%s\"\n", p);
    p = "456"+1;        
    printf("p = \"%s\"\n", p);
 
    return 0;
}
//输出“56”，p指向的地址+1后，往后移了一位，读到的内容从“456”变成了“56\0".

练习11-2

#include <stdio.h>
 
#define str_add(arr) ((sizeof(arr)) / (sizeof(arr[0])))
int main(void)
{
    char s[][5] = { "LISP","C","Ada" };
    char* p[] = { "PAUL","X","MAC","PC","Linux" };
    
    int i;
    int x = str_add(s);
    int y = str_add(p);
 
    for (i = 0; i < x; i++) {
        printf("x = \"%s\"\n",s[i]);
    }
 
    for (i = 0; i < y; i++) {
        printf("x = \"%s\"\n",p[i]);
    }
    return 0;
}

练习11-3

 
#include <stdio.h>
 
/*--- 将字符串s复制到d ---*/
char* str_copy(char* d, const char* s)
{
    char* t = d;
 
    while (*d++ = *s++)
        ;
    return t;
}
 
int main(void)
{
    char str[128] = "ABC";
    char tmp[128];
 
    printf("str = \"%s\"\n", str);
 
    printf("复制的是：", tmp);
    scanf("%s", tmp);
 
    
 
    puts("复制了。");
    printf("str = \"%s\"\n", str_copy(str, tmp));
 
    return 0;
}

练习11-4

#include <stdio.h>
 
void put_string(const char* s) 
{
    putchar(*s);
    while (*s++)
    {
        putchar(*s);
    }    
}
 
int main()
{
    char s[123] ;
    printf("请输入字符串:");
    scanf("%s",s);
    put_string(s);
    return 0;
}

练习11-5

#include <stdio.h>
 
int str_chnum(const char* s, int c)
{
    int cnt = 0;
    while (*s)    // while (*s != NULL)
    {
        if (*s == c)
        {
            cnt += 1;
        }
        *s++;
    }
    return cnt;
}
 
int main(void)
{
    char str[128];
    char cx;
 
    printf("请输入要查找的字符：");
    scanf("%c", &cx);
    printf("请输入一个字符串：");	
    scanf("%s", str);
 
    printf("字符串\"%s\"中字符要找的个数为%d\n", str, str_chnum(str, cx));
 
    return 0;
}

练习11-6

意思是：输入要找的 a 字符，在字符串 bash 中，输出结果是ash；在bdsadasd中含有多个a

以最先出现的为准，结果是adasd

#include <stdio.h>
 
char* str_chnum(const char* s, int c) 
{
    while (*s++) 
    {
        char* t = s;
 
        if (*s == c) {
            return     t;
            break;
        }
    }
    return NULL;
}
 
int main() {
    char s[128];
    char c;
    printf("要计数的字符是：");
    scanf("%c", &c);
    printf("请输入字符串:");
    scanf("%s", s);
 
    printf("%s", str_chnum(s, c));
 
    return 0;
}

练习11-7

#include <ctype.h>
#include <stdio.h>
 
/*--- 将字符串中的英文字符转为大写字母 ---*/
void str_toupper(char* s)
{
    while (*s)
    {
        *s = toupper(*s);
        *s++;
    }
}
 
/*--- 将字符串中的英文字符转为小写字母 ---*/
void str_tolower(char* s)
{
    while (*s)
    {
        *s = tolower(*s);
        *s++;
    }
}
 
int main()
{
    char str[128];
 
    printf("请输入字符串：");
    scanf("%s", str);
 
    str_toupper(str);
    printf("大写字母：%s\n", str);
 
    str_tolower(str);
    printf("小写字母：%s\n", str);
 
    return 0;
}

练习11-8

#include <stdio.h>
 
void del_digit(char* ptr)
{
	char temp[128];
	char* p = temp;
 
	while (*ptr != NULL)
	{
		if (*ptr < '0' || *ptr>'9')
		{
			*p = *ptr;
			 p++;
		}
		ptr++;
	}
 
	*p = '\0';
	printf("%s", temp);
}
 
int main()
{
	char str[128];
 
	printf("输入字符串str = ");
	scanf("%s", str);
 
	printf("字符串%s删除数字后为：", str);
	del_digit(str);
 
	return 0;
}

练习11-9

#include <stdio.h>
#include <string.h>
 
void str_renull(char* ptr)
{
	while (*ptr)
	{
		*ptr = '\0';
		ptr++;
	}
}
int main()
{
	char str1[128];
	char str2[128];
	char temp[128];
	int n;
 
	printf("输入字符串str1 = ");	scanf("%s", str1);
	printf("输入字符串str2 = ");	scanf("%s", str2);
	printf("n = ");		scanf("%d", &n);
 
	printf("str1长度为%d。\n", strlen(str1));
	printf("str2长度为%d。\n", strlen(str2));
 
	printf("temp复制str1(all) = \"%s\"。\n", strcpy(temp, str1));
	str_renull(temp);
	printf("temp复制str2(%d) = \"%s\"。\n", n, strncpy(temp, str2, n));
	str_renull(temp);
	strcpy(temp, str1);
 
	printf("str1(all) & str2(all) = \"%s\"。\n", strcat(str1, str2));
	strcpy(str1, temp);
	printf("str1 & str2(%d) = \"%s\"。\n", n, strncat(str1, str2, n));
 
	strcpy(str1, temp);
	printf("str1(all) - str2(all) = %d。\n", strcmp(str1, str2));
	printf("str1(%d) - str2(%d) = %d。\n", n, n, strncmp(str1, str2, n));
 
	return 0;
}

练习11-10

//编写函数，实现atoi()、atol()、atof()三个函数的功能
#include <stdio.h>
#include <limits.h>
 
int strtoi(const char* nptr)
{
	int result = 0;
	int sign = 1;
 
	if (*nptr == '-')
	{
		sign = -1;
		nptr++;
	}
	if (*nptr == '+')
	{
		nptr++;
	}
 
	while (*nptr)
	{
		result = result * 10 + (*nptr) - '0';
		nptr++;
	}
 
	return result * sign;
}
 
long strtol(const char* nptr)
{
	long result = 0;
	int sign = 1;
 
	if (*nptr == '-')
	{
		sign = -1;
		nptr++;
	}
	if (*nptr == '+')
	{
		nptr++;
	}
 
	while (*nptr)
	{
		result = result * 10 + (*nptr) - '0';
		nptr++;
	}
 
	return result * sign;
}
 
double strtof(const char* nptr)
{
	double result = 0.0;
	double n = 1.0;
	int sign = 1;
 
	if (*nptr == '-')
	{
		sign = -1;
		nptr++;
	}
	if (*nptr == '+')
	{
		nptr++;
	}
 
	while (*nptr)
	{
		if (*nptr == '.')
		{
			nptr++;
			break;
		}
 
		result = result * 10 + (*nptr) - '0';
		nptr++;
	}
 
	while (*nptr)
	{
		n /= 10.0;
		result = result + ((*nptr) - '0') * n;
		nptr++;
	}
 
	return result * sign;
}
 
int main()
{
	char str_int[128];
	char str_long[128];
	char str_double[128];
 
	printf("整形str_int = ");	scanf("%s", str_int);
	printf("长整型str_long = ");	scanf("%s", str_long);
	printf("双精度浮点型str_double = ");	scanf("%s", str_double);
 
	printf("转换之后\n");
 
	printf("\"%s\" => int型  = %d。\n", str_int, strtoi(str_int));
	printf("\"%s\" => long型 = %ld。\n", str_long, strtol(str_long));
	printf("\"%s\" => double型 = %.10lf。\n", str_double, strtof(str_double));
 
	return 0;
}