c++ primer 练习 3.37、3.38、3.39、3.40

3.37

#include<iostream>using std::cout;using std::cin;using std::endl;int main(){    const char ca[] = {'h', 'e', 'l', 'l', 'o'};    const char *cp = ca;    while (*cp) {        cout << *cp << endl;        ++cp;    }    return 0;}

out：

helloa

3.38

纯属搬运

Pointer addition is forbidden in C++, you can only subtract two pointers.The reason for this is that subtracting two pointers gives a logically explainable result - the offset in memory between two pointers. Similarly, you can subtract or add an integral number to/from a pointer, which means "move the pointer up or down". Adding a pointer to a pointer is something which is hard to explain. What would the resulting pointner represent?If by any chance you explicitly need a pointer to a place in memory whose address is the sum of some other two addresses, you can cast the two pointers to int, add ints, and cast back to a pointer. Remember though, that this solution needs huge care about the pointer arithmetic and is something you really should never do.

3.39

1

#include<iostream>using std::cout;using std::cin;using std::endl;#include<cstring>int main(){    const char ca1[] = "string-A";    const char ca2[] = "string-B";    if (strcmp(ca1 , ca2) > 0) {        cout << "string-A big" << endl;    } else {        cout << "string-B big" << endl;    }    return 0;}

2

#include<iostream>using std::cout;using std::cin;using std::endl;#include<string>using std::string;int main(){    string s1 = "string-A";    string s2 = "string-B";    cout << "Big one is: ";    if (s1 > s2) {        cout << s1 << endl;    } else {        cout << s2 << endl;    }    return 0;}

3.40

#include<cstring>#include<iostream>using std::cout;using std::cin;using std::endl;int main(){    char s1[100] = "stringA";    char s2[] = "stringB";    strcat(s1 , s2);    char s[100];    strcpy(s , s1);    cout << s << endl;    return 0;}