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ch03/README.md

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-##Exercise 3.1 : [part1](ex3_1a.cpp) | [part2](ex3_1b.cpp)##Exercise 3.2 : [part1](ex3_2a.cpp) | [part2](ex3_2b.cpp)##Exercise 3.3>Explain how whitespace characters are handled in the stringinput operator and in the getline function.The `getline` function takes an input stream and a string.This function reads the given stream up to and includingthe first newline and stores what it read—not includingthe newline—in its string argument.After getline sees a newline, even if it is the first character in the input,it stops reading and returns.If the first character in the input is a newline,then the resulting string is the empty string.`getline` function whitespace handling,do not ignore the beginning of the line blank characters read charactersuntil it encounters a line break,read to termination and discard newline(line breaks removed from the input stream  but is not stored in the string object).[Read more](http://www.cplusplus.com/reference/string/string/getline/)##Exercise 3.4 : [part1](ex3_4a.cpp) | [part2](ex3_4b.cpp)##Exercise 3.5 : [part1](ex3_5a.cpp) | [part2](ex3_5b.cpp)##[Exercise 3.6](ex3_6.cpp)##Exercise 3.7>What would happen if you define the loop control variable in the previousexercise as type char? Predict the results and then change your programto use a char to see if you were right.No different.    auto& c : strWe use `auto` to let the compiler determine the type of `c`.which in this case will be `char&`.##[Exercise 3.8](ex3_8.cpp)##Exercise 3.9>What does the following program do? Is it valid? If not, why not?```cppstring s;cout << s[0] << endl;```invalid in theory, but the compiler passes.`s` is empty, so `s[0]` is undefined. But the compiler always define `s[0]`with `\0`, so you can use `s[0]` in the `cout`.##[Exercise 3.10](ex3_10.cpp)##Exercise 3.11>Is the following range for legal? If so, what is the type of c?```cppconst string s = "Keep out!";for (auto &c : s){/*... */}```When you don't change `c`'s value, it's legal, else it's illegal.For example:    cout << c;  // legal.    c = 'X';    // illegal.The type of `c` is `const char&`. read-only variable is not assignable.##Exercise 3.12>Which, if any, of the following vector definitions are in error?For those that are legal, explain what the definition does.For those that are not legal, explain why they are illegal.```cppvector<vector<int>> ivec;         // legal(c++11), vectors.vector<string> svec = ivec;       // illegal, different type.vector<string> svec(10, "null");  // legal, vector have 10 strings: "null".```##Exercise 3.13>How many elements are there in each of the followingvectors? What are the values of the elements?```cppvector<int> v1;         // size:0,  no values.vector<int> v2(10);     // size:10, value:0vector<int> v3(10, 42); // size:10, value:42vector<int> v4{10};     // size:1,  value:10vector<int> v5{10, 42}; // size:2,  value:10, 42vector<string> v6{10};  // size:10, value:""vector<string> v7{10, "hi"};  // size:10, value:"hi"```##[Exercise 3.14](ex3_14.cpp)##[Exercise 3.15](ex3_15.cpp)##[Exercise 3.16](ex3_16.cpp)##[Exercise 3.17](ex3_17.cpp)##[Exercise 3.18](ex3_18.cpp)##[Exercise 3.19](ex3_19.cpp)##[Exercise 3.20](ex3_20.cpp)##[Exercise 3.21](ex3_21.cpp) ([Generics Version](ex3_21_generics_version))##[Exercise 3.22](ex3_22.cpp)##[Exercise 3.23](ex3_23.cpp)##[Exercise 3.24](ex3_24.cpp)##[Exercise 3.25](ex3_25.cpp)##Exercise 3.26>In the binary search program on page 112,why did we write `mid=beg+(end-beg)/2;` instead of `mid=(beg+end) /2;`?Because the iterator of vector don't define the `+` operator **between the two iterators**.`beg + end` is illegal.We can only use the subtraction between the two iterators.##Exercise 3.27>Assuming txt_size is a function that takes no argumentsand returns an int value, which of the following definitions are illegal?Explain why.```cppunsigned buf_size = 1024;int ia[buf_size];   // legalint ia[4 * 7 - 14]; // legalint ia[txt_size()]; // legalchar st[11] = "fundamental";  // illegal, the string's size is 12.```##Exercise 3.28>What are the values in the following arrays?```cppstring sa[10];int ia[10];int main() {  string sa2[10];  int ia2[10];}```please see 2.2.1. Variable Definitions -> Default Initialization.`std::string` isn't a build-in type. The initializer will set it empty.`ia` and `ia2` are build-type. But `ia` isn't in the function body, so itwill be initalized to **zero**. `ia2` is in the function body. so it'svalue is **undefined**.You can also use gdb to debug the value when the code is running.##Exercise 3.29:>List some of the drawbacks of using an array instead of a vector.1. can't add elements to an array.2. can't use auto to deduce the type from a list of initalizers.3. no arrays of references.4. can't use template and iterator.5. vector have lots of useful methods and algorithms.##Exercise 3.30>Identify the indexing errors in the following code:```cppconstexpr size_t array_size = 10;int ia[array_size];for (size_t ix = 1; ix <= array_size; ++ix)      ia[ix] = ix;```The size of ia is 10, so the index of value should less than 10.ix **cannot** equal the array_size.##[Exercise 3.31](ex3_31.cpp)##[Exercise 3.32](ex3_32.cpp)##Exercise 3.33>What would happen if we did not initialize the scores array in the programon page 116?If we did not initialize the scores array. the array is undefined. the valuewill be Unknown.Look like this:![result](https://db.tt/3T4TQoo8)##Exercise 3.34>Given that p1 and p2 point to elements in the same array, what does the following code do?Are there values of p1 or p2 that make this code illegal?```cppp1 += p2 - p1;```we assume p1 and p2 point to an array arr. so `p1 = &arr[0]`; and `p2 = &arr[0]`.p2 - p1 is the distance of arr[0] to arr[0], and must be zero.so `p1 += 0;` can not change the p1's point.`p1 += p2 - p1;` same as `p1 = p2;`. If p2 and p1 are legal, this code always legal.##[Exercise 3.35](ex3_35.cpp)##[Exercise 3.36](ex3_36.cpp)##Exercise 3.37>What does the following program do?```cppconst char ca[] = {'h', 'e', 'l', 'l', 'o'};const char *cp = ca;while (*cp) {    cout << *cp << endl;    ++cp;}```Print all the elements of the array.##Exercise 3.38>In this section, we noted that it was not only illegal but meaningless to try to add two pointers.Why would adding two pointers be meaningless?Because Subtracting two points gives a logically explainable result - the offsetin memory between two points. 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 toexplain. The result is meaningless.----References:- [Why can't I add pointers](http://stackoverflow.com/questions/2935038/why-cant-i-add-pointers)##[Exercise 3.39](ex3_39.cpp)##[Exercise 3.40](ex3_40.cpp)##[Exercise 3.41](ex3_41.cpp)##[Exercise 3.42](ex3_42.cpp)##[Exercise 3.43](ex3_43.cpp)##[Exercise 3.44](ex3_44.cpp)##[Exercise 3.45](ex3_45.cpp)
+##Exercise 3.1 : [part1](ex3_1a.cpp) | [part2](ex3_1b.cpp)##Exercise 3.2 : [part1](ex3_2a.cpp) | [part2](ex3_2b.cpp)##Exercise 3.3>Explain how whitespace characters are handled in the stringinput operator and in the getline function.The `getline` function takes an input stream and a string.This function reads the given stream up to and includingthe first newline and stores what it read—not includingthe newline—in its string argument.After getline sees a newline, even if it is the first character in the input,it stops reading and returns.If the first character in the input is a newline,then the resulting string is the empty string.`getline` function whitespace handling,do not ignore the beginning of the line blank characters read charactersuntil it encounters a line break,read to termination and discard newline(line breaks removed from the input stream  but is not stored in the string object).[Read more](http://www.cplusplus.com/reference/string/string/getline/)##Exercise 3.4 : [part1](ex3_4a.cpp) | [part2](ex3_4b.cpp)##Exercise 3.5 : [part1](ex3_5a.cpp) | [part2](ex3_5b.cpp)##[Exercise 3.6](ex3_6.cpp)##Exercise 3.7>What would happen if you define the loop control variable in the previousexercise as type char? Predict the results and then change your programto use a char to see if you were right.No different.    auto& c : strWe use `auto` to let the compiler determine the type of `c`.which in this case will be `char&`.##[Exercise 3.8](ex3_8.cpp)##Exercise 3.9>What does the following program do? Is it valid? If not, why not?```cppstring s;cout << s[0] << endl;```invalid in theory, but the compiler passes.`s` is empty, so `s[0]` is undefined. But the compiler always define `s[0]`with `\0`, so you can use `s[0]` in the `cout`.##[Exercise 3.10](ex3_10.cpp)##Exercise 3.11>Is the following range for legal? If so, what is the type of c?```cppconst string s = "Keep out!";for (auto &c : s){/*... */}```When you don't change `c`'s value, it's legal, else it's illegal.For example:    cout << c;  // legal.    c = 'X';    // illegal.The type of `c` is `const char&`. read-only variable is not assignable.##Exercise 3.12>Which, if any, of the following vector definitions are in error?For those that are legal, explain what the definition does.For those that are not legal, explain why they are illegal.```cppvector<vector<int>> ivec;         // legal(c++11), vectors.vector<string> svec = ivec;       // illegal, different type.vector<string> svec(10, "null");  // legal, vector have 10 strings: "null".```##Exercise 3.13>How many elements are there in each of the followingvectors? What are the values of the elements?```cppvector<int> v1;         // size:0,  no values.vector<int> v2(10);     // size:10, value:0vector<int> v3(10, 42); // size:10, value:42vector<int> v4{10};     // size:1,  value:10vector<int> v5{10, 42}; // size:2,  value:10, 42vector<string> v6{10};  // size:10, value:""vector<string> v7{10, "hi"};  // size:10, value:"hi"```##[Exercise 3.14](ex3_14.cpp)##[Exercise 3.15](ex3_15.cpp)##[Exercise 3.16](ex3_16.cpp)##[Exercise 3.17](ex3_17.cpp)##[Exercise 3.18](ex3_18.cpp)##[Exercise 3.19](ex3_19.cpp)##[Exercise 3.20](ex3_20.cpp)##[Exercise 3.21](ex3_21.cpp) ([Generics Version](ex3_21_generics_version))##[Exercise 3.22](ex3_22.cpp)##[Exercise 3.23](ex3_23.cpp)##[Exercise 3.24](ex3_24.cpp)##[Exercise 3.25](ex3_25.cpp)##Exercise 3.26>In the binary search program on page 112,why did we write `mid=beg+(end-beg)/2;` instead of `mid=(beg+end) /2;`?Because the iterator of vector don't define the `+` operator **between the two iterators**.`beg + end` is illegal.We can only use the subtraction between the two iterators.##Exercise 3.27>Assuming txt_size is a function that takes no argumentsand returns an int value, which of the following definitions are illegal?Explain why.```cppunsigned buf_size = 1024;int ia[buf_size];   // legalint ia[4 * 7 - 14]; // legalint ia[txt_size()]; // legalchar st[11] = "fundamental";  // illegal, the string's size is 12.```##Exercise 3.28>What are the values in the following arrays?```cppstring sa[10];int ia[10];int main() {  string sa2[10];  int ia2[10];}```please see 2.2.1. Variable Definitions -> Default Initialization.`std::string` isn't a build-in type. The initializer will set it empty.`ia` and `ia2` are build-type. But `ia` isn't in the function body, so itwill be initalized to **zero**. `ia2` is in the function body. so it'svalue is **undefined**.You can also use gdb to debug the value when the code is running.##Exercise 3.29:>List some of the drawbacks of using an array instead of a vector.1. can't add elements to an array.2. can't use auto to deduce the type from a list of initalizers.3. no arrays of references.4. can't use template and iterator.5. vector have lots of useful methods and algorithms.##Exercise 3.30>Identify the indexing errors in the following code:```cppconstexpr size_t array_size = 10;int ia[array_size];for (size_t ix = 1; ix <= array_size; ++ix)      ia[ix] = ix;```The size of ia is 10, so the index of value should less than 10.ix **cannot** equal the array_size.##[Exercise 3.31](ex3_31.cpp)##[Exercise 3.32](ex3_32.cpp)##Exercise 3.33>What would happen if we did not initialize the scores array in the programon page 116?If we did not initialize the scores array. the array is undefined. the valuewill be Unknown.Look like this:![result](https://db.tt/3T4TQoo8)##Exercise 3.34>Given that p1 and p2 point to elements in the same array, what does the following code do?Are there values of p1 or p2 that make this code illegal?```cppp1 += p2 - p1;```we assume p1 and p2 point to an array arr. so `p1 = &arr[0]`; and `p2 = &arr[0]`.p2 - p1 is the distance of arr[0] to arr[0], and must be zero.so `p1 += 0;` can not change the p1's point.`p1 += p2 - p1;` same as `p1 = p2;`. If p2 and p1 are legal, this code always legal.##[Exercise 3.35](ex3_35.cpp)##[Exercise 3.36](ex3_36.cpp)##Exercise 3.37>What does the following program do?```cppconst char ca[] = {'h', 'e', 'l', 'l', 'o'};const char *cp = ca;while (*cp) {    cout << *cp << endl;    ++cp;}```Print all the elements of the array.WARNING!!!!When we use a string, the compiler put it in the section .rodata, the code uses C-style character string without adding a '\0' in the end of ca.So, when we code like this:```cppconst char ca[] = {'h', 'e', 'l', 'l', 'o'};const char s[] = "world";const char *cp = ca;while (*cp) {cout << *cp;++cp;}```The code will print "helloworld" when you run it. because the charater list in the .rodata like this:h e l l o w o r l d \0While(*cp) judge wether *cp is 0 or not. when *cp is not 0, it will print the character until 0.When you change the code like this:const char ca[] = {'h', 'e', 'l', 'l', 'o', '\0'};the charater list in the .rodata:h e l l o \0 w o r l d \0The program will run correctly. So when using C-style character string, be careful!!##Exercise 3.38>In this section, we noted that it was not only illegal but meaningless to try to add two pointers.Why would adding two pointers be meaningless?Because Subtracting two points gives a logically explainable result - the offsetin memory between two points. 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 toexplain. The result is meaningless.----References:- [Why can't I add pointers](http://stackoverflow.com/questions/2935038/why-cant-i-add-pointers)##[Exercise 3.39](ex3_39.cpp)##[Exercise 3.40](ex3_40.cpp)##[Exercise 3.41](ex3_41.cpp)##[Exercise 3.42](ex3_42.cpp)##[Exercise 3.43](ex3_43.cpp)##[Exercise 3.44](ex3_44.cpp)##[Exercise 3.45](ex3_45.cpp)