C语言课后习题练习（四）

(ps:提前声明一下：课后习题是备份给自己看的😂)

1.输入3个整数，按由小到大的顺序输出

int main() {
    void swap(int *p1, int * p2);
    int n1, n2, n3;
    int *p1, *p2, *p3;
    printf("input three integer n1,n2,n3:");
    scanf("%d,%d,%d",&n1,&n2,&n3);
    p1 = &n1;
    p2 = &n2;
    p3 = &n3;
    if (n1 > n2)
        swap(p1, p2);
    if (n1 > n3)
        swap(p1, p3);
    if (n2 > n3)
        swap(p2, p3);
    printf("Now,the order is:%d,%d,%d\n",n1,n2,n3);
    
    return 0;
}

void swap(int *p1, int *p2) {
    int p;
    p = *p1;
    *p1 = *p2;
    *p2 = p;
}

远行结果： c1.png

2.输入三个字符串，按由小到大的顺序输出

//记得导入头文件:#import <string.h>
int main() {
    void swap(char *, char *);
    char str1[20],str2[31],str3[20];
    printf("input three line:\n");
    gets(str1);
    gets(str2);
    gets(str3);
    if (strcmp(str1, str2) > 0)
        swap(str1, str2);
    if (strcmp(str1, str3) > 0)
        swap(str1, str3);
    if (strcmp(str2, str3) > 0)
        swap(str2, str3);
    printf("Now,the order is:\n");
    printf("%s\n%s\n%s\n",str1,str2,str3);
    return 0;
}

void swap(char *p1, char *p2){
    char p[20];
    strcpy(p, p1);
    strcpy(p1, p2);
    strcpy(p2, p);
}

运行结果： c2.png

（注：在Xcode中运行才显示的warning: this program uses gets(), which is unsafe.关于使用gets()不安全的警告）

3.写一函数，求一个字符串的长度。在main函数中输入字符串，并输入其长度

int main() {
    int length(char *p);
    int len;
    char str[20];
    printf("input string: ");
    scanf("%s",str);
    len = length(str);
    printf("The length of string is %d. \n",len);
    return 0;
}

int length(char *p) {          //求字符串长度函数
    int n = 0;
    while (*p != '\0') {
        n++;
        p++;
    }
    return(n);
}

运行结果： c3.png

4.有一字符串，包含n个字符。写一函数，将此字符串中从第m个字符开始的全部字符复制成为另一个字符串

//记得导入头文件:#import <string.h>
int main() {
    void copystr(char *, char *, int);
    int m;
    char str1[20],str2[20];
    printf("input string:\n");
    gets(str1);
    printf("which character that begin to copy?");
    scanf("%d",&m);
    if (strlen(str1) < m)
        printf("input error!");
    else {
        copystr(str1, str2, m);
        printf("result:%s\n",str2);
    }
    return 0;
}

void copystr(char *p1, char *p2, int m) {     //字符串部分复制函数
    int n = 0;
    while (n < m - 1) {
        n++;
        p1++;
    }
    while (*p1 != '\0') {
        *p2 = *p1;
        p1++;
        p2++;
    }
    *p2 = '\0';
}

运行结果： c4.png

（注：在Xcode中运行才显示的warning: this program uses gets(), which is unsafe.关于使用gets()不安全的警告）

5.输入一行文字，找出其中大写字母、小写字母、空格、数字以及其他字符各有多少

//记得导入头文件:#import <string.h>
int main() {
    int upper = 0, lower = 0, digit = 0, space = 0, other = 0, i = 0;
    char *p,s[20];
    printf("input string: ");
    while ((s[i] = getchar()) != '\n')
        i++;
    p = &s[0];
    while (*p != '\n') {
        if (('A' <= *p) && (*p <= 'Z'))
            ++upper;
        else if (('a' <= *p) && (*p <= 'z'))
            ++lower;
        else if (*p == ' ')
            ++space;
        else if ((*p <= '9') && (*p >= '0'))
            ++digit;
        else
            ++other;
        p++;
    }
    printf("upper case:%d    lower case:%d",upper,lower);
    printf("    space:%d    digit:%d    other:%d\n",space,digit,other);
    return 0;
}

运行结果： c5.png

6.将n个数按输入时顺序的逆序排列，用函数实现

int main() {
    void sort(char *p, int m);
    int i, n;
    char *p, num[20];
    printf("input n:");
    scanf("%d",&n);
    printf("please input these numbers:\n");
    for (i = 0; i < n; i++)
        scanf("%d",&num[i]);
    p = &num[0];
    sort(p, n);
    printf("Now,the sequence is:\n");
    for (i = 0; i < n; i++)
        printf("%d",num[i]);
    printf("\n");
    return 0;
}

void sort(char *p, int m) {       //将n个逆序排列函数
    int i;
    char temp, *p1, *p2;
    for (i = 0; i < m/2; i++) {
        p1 = p + i;
        p2 = p + (m - 1 - i);
        temp = *p1;
        *p1 = *p2;
        *p2 = temp;
    }
}

运行结果： c6.png