C++ Primer #01 Getting Started

1. CHAPTER 1 GETTING STARTED

1.1 Writing a Simple C++ Program

Exercise 1.2:

Change the program to return -1. A return value of -1 is often treated as an indicator that the program failed. Recompile and rerun your program to see how your system treats a failure indicator from main.

---

Return -1:

C++ code:

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#include <iostream>
​
using namespace std;
​
int main()
{
    std::cout << "Hello world!" << std::endl;
​
    return -1;
}
​

Console:

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Hello world!
​
Process returned -1 (0xFFFFFFFF)   execution time : 1.729 s
Press any key to continue.

Return 0:

C++ code:

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#include <iostream>
​
using namespace std;
​
int main()
{
    std::cout << "Hello world!" << std::endl;
​
    return 0;
}

Console:

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Hello world!
​
Process returned 0 (0x0)   execution time : 6.631 s
Press any key to continue.

1.2 A First Look at Input/Output

Exercise 1.4:

Our program used the addition operator, +, to add two numbers. Write a program that uses the multiplication operator, *, to print the product instead.

---

C++ code:

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#include <iostream>
​
using namespace std;
​
int main()
{
​
    std::cout << "Enter two numbers:"  << std::endl;
    int num1, num2;
    std::cin >> num1 >> num2;
    std::cout << "The product of " << num1 << " and " << num2 << " is " <<
    num1*num2 << std::endl;
​
    return 0;
}

Shell:

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Enter two numbers:
10
28
The product of 10 and 28 is 280
​
Process returned 0 (0x0)   execution time : 40.071 s
Press any key to continue.

Exercise 1.6

Explain whether the following program fragment is legal.

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std::cout << "The sum of " << v1; 
          << " and " << v2; 
          << " is " << v1 + v2 << std::endl;

If the program is legal, what does it do? If the program is not legal, why not? How would you fix it?

---

Answer:

This program is not legal. Because there are 3 semicolons in between the source code which is unable for the compiler to compile. The fixed code is the following:

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std::cout << "The sum of " << v1
          << " and " << v2
          << " is " << v1 + v2 << std::endl;

1.3 A Word about Comments

Exercise 1.8:

Indicate which, if any, of the following output statements are legal:

---

✔️

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std::cout << "/*";

It prints out: /*

---

✔️

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std::cout << "*/";

It prints out: */

---

✔️

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std::cout << /* "*/" */;

It prints out: /*

---

✔️

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std::cout << /* "*/" /* "/*" */;

It prints out: /*

1.4 Flow of Control

Exercise 1.9

Write a program that uses a while to sum the numbers from 50 to 100.

---

Code:

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#include <iostream>
​
using namespace std;
​
int main()
{
​
    int sum = 0, add = 50;
    while(add <= 100){
        sum+=add;
        add++;
    }
    std::cout << "The sum from 50 to 100 is: " << sum << std::endl;
​
    return 0;
}
​

Console:

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The sum from 50 to 100 is: 3825
​
Process returned 0 (0x0)   execution time : 0.103 s
Press any key to continue.

Exercise 1.10:

In addition to the ++ operator that adds 1 to its operand, there is a decrement operator (--) that subtracts 1. Use the decrement operator to write a while that prints the numbers from ten down to zero.

---

Code:

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#include <iostream>
​
using namespace std;
​
int main()
{
​
    int num = 10;
    while(num >= 0){
        std::cout << num << " ";
        num--;
    }
​
    return 0;
}
​

Console:

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10 9 8 7 6 5 4 3 2 1 0
Process returned 0 (0x0)   execution time : 0.104 s
Press any key to continue.

Exercise 1.11

Write a program that prompts the user for two integers. Print each number in the range specified by those two integers.

---

Code:

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#include <iostream>
​
using namespace std;
​
int main()
{
    int num1, num2;
    std::cout << "Please enter two number: " << std::endl;
    std::cin >> num1 >> num2;
    int big, small;
    if(num1>num2){
            big = num1;
            small = num2;
    }
    else{
            big = num2;
            small = num1;
    }
    std::cout << "The range of two value is: " << std::endl;
    while(small<=big){
        std::cout << small << " ";
        small++;
    }
​
    return 0;
}

Console:

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Please enter two number:
10
28
The range of two value is:
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
Process returned 0 (0x0)   execution time : 8.490 s
Press any key to continue.

Exercise 1.13

Rewrite the first two exercises from § 1.4.1 (p. 13) using for loops.

---

Rewrite 1.10:

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#include <iostream>
​
using namespace std;
​
int main()
{
    for(int num=10; num >=0; num--){
        std::cout << num << " ";
    }
​
    return 0;
}

Rewrite 1.11:

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#include <iostream>
​
using namespace std;
​
int main()
{
    int num1, num2;
    std::cout << "Please enter two number: " << std::endl;
    std::cin >> num1 >> num2;
    int big, small;
    if(num1>num2){
            big = num1;
            small = num2;
    }
    else{
            big = num2;
            small = num1;
    }
    std::cout << "The range of two value is: " << std::endl;
​
    for(small; small<=big; small++){
        std::cout << small << " ";
    }
​
    return 0;
}
​

⚠️There is another solution which specify the start and end(aka. user defines the small and big)

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#include <iostream>
​
using namespace std;
​
int main()
{
    int start_val, end_val;
    std::cout << "Please enter the start and end of the range" << std::endl;
    std::cin >> start_val >> end_val;
    std::cout << "The range of two value is: ";
​
    while(start_val<=end_val){
        std::cout << start_val++ << " ";
    }
​
    return 0;
}
​

You can even increment the value inside the loop:

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    while(start_val<=end_val){
        std::cout << start_val++ << " ";
    }

Exercise 1.16

Write your own version of a program that prints the sum of a set of integers read from cin.

---

Oh my dear lord, I can't believe the method can works:

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#include <iostream>
​
using namespace std;
​
int main()
{
    int sum = 0, value = 0;
    std::cout << "Starting..." << std::endl;
    for(sum; std::cin >> value; sum+=value){
​
    }
    std::cout << "The sum of all your numbers typed in is: " << sum << std::endl;
​
    return 0;
}
​

⚠️ Notice the for loop!!! Actually it makes sense once you take a breath and think. So the first argument sum is just an initial, std::cin >> value is always true until you exit, sum+=value is the incrementation. Cooooooool!!!

Example 1.4.4

Although this is not an exercise, it still deserves for a note. The program is expected to do the following:

If I input 10 10 10 28 28, it will prompt a message that 10 occurs 3 times right after I typed 28.

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#include <iostream>
​
using namespace std;
​
int main()
{
    std::cout << "Starting..." << std::endl;  //Start
​
    int current_val, input_val; //Declare 2 values
    int count_times = 0;
    //current_val is the first parameter to feed which make sure we have something
    if(std::cin >> current_val){
            count_times = 1;  //start counting
            while(std::cin >> input_val){
                if(input_val == current_val){
                    count_times++;  //if the next input is ok, count++
                }else{
                    //otherwise, print out what is the number and its count right now
                    std::cout << current_val << " occurs " << count_times << " times." << std::endl;
                    count_times = 1;
                    current_val = input_val;
                }
            }
            //similar to the else block
            std::cout << current_val << " occurs " << count_times << " times." << std::endl;
    }
    return 0;
}
​

Console:

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Starting...
1994
10
1994 occurs 1 times.
10
28
10 occurs 2 times.
28
28
28
28
28
^Z
28 occurs 6 times.
​
Process returned 0 (0x0)   execution time : 26.917 s
Press any key to continue.

1.5 Introducing Classes

Exercise 1.20:

http://www.informit.com/title/0321714113 contains a copy of Sales_item.h in the Chapter 1 code directory. Copy that file to your working directory. Use it to write a program that reads a set of book sales transactions, writing each transaction to the standard output.

---

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#include <iostream>
#include "Sales_item.h"
​
using namespace std;
​
using std::cin;  //similar to python's "import xx as xx"
using std::cout;
using std::endl;
​
int main()
{
    cout << "Starting..." << endl;
    for (Sales_item item; cin >> item; cout << "Transaction: " << item << endl);
    return 0;
}
​

Console:

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Starting...
0-201-78345-X
3
20.00
Transaction: 0-201-78345-X 3 60 20
9788842069102
2
35
Transaction: 9788842069102 2 70 35
^Z
​
Process returned 0 (0x0)   execution time : 199.145 s
Press any key to continue.

Exercise 1.21:

Write a program that reads two Sales_item objects that have the same ISBN and produces their sum.

---

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#include <iostream>
#include "Sales_item.h"
​
using namespace std;
​
using std::cin;  
using std::cout;
using std::endl;
​
int main()
{
    cout << "First Transaction: " << endl;
    Sales_item item1;
    cin >> item1;
​
    cout << "Second Transaction: " << endl;
    Sales_item item2;
    cin >> item2;
​
    if(item1.isbn() == item2.isbn()){
        cout<< item1+item2 << endl;
    }
​
    return 0;
}
​

Console:

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First Transaction:
1-86092-042-X
5
10.00
Second Transaction:
1-86092-042-X
10
12.00
1-86092-042-X 15 170 11.3333
​
Process returned 0 (0x0)   execution time : 44.223 s
Press any key to continue.

⚠️ There is something missing from the above code: the else code block.

Hence we should add the following:

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    if(item1.isbn() == item2.isbn()){
        cout << item1+item2 << endl;
        return 0;
    }else{
        cerr << "The ISBN of transaction is different!";
        return -1;
    }

The full version should be:

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First Transaction:
1-86092-042-X
5
20.00
Second Transaction:
1-86092-004-7
3
15.00
The ISBN of transaction is different!
Process returned -1 (0xFFFFFFFF)   execution time : 59.879 s
Press any key to continue.

1.6 The Bookstore Program

This is the code example of this section. However, I wrote something wrong which might be helpful for me to better understand and revise the code.

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#include <iostream>
#include "Sales_item.h"
​
using std::cout;
using std::cin;
using std::endl;
using std::cerr;
​
int main()
{
    cout << "Transaction program starts... You can fill the data now: " << endl;
    Sales_item total_item;
    if(cin >> total_item){
​
        int transaction_counts = 1;
        Sales_item processing_item;
        while(cin >> processing_item){
​
        if(total_item.isbn() == processing_item.isbn()){
            transaction_counts++;
        }else{
            total_item+=processing_item;
            cout << "The transaction of " << total_item.isbn() << " occurs " << transaction_counts << " times." << endl;
            transaction_counts = 1;
            total_item = processing_item;
              }
        }   cout << "The transaction of " << total_item.isbn() << " occurs " << transaction_counts << " times." << endl;
        return 0;
    }else{
        cerr << "There is no transaction feeding in!" << endl;
        return -1;
    }
}
​

Console:

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Transaction program starts... You can fill the data now:
1-86092-042-X
10
25.00
1-86092-042-X
5
30.00
1-86092-004-7
20
15.00
The transaction of 1-86092-042-X occurs 2 times.
^Z
The transaction of 1-86092-004-7 occurs 1 times.
​
Process returned 0 (0x0)   execution time : 41.402 s
Press any key to continue.

1. ❌The return value of 0 should not be inside the outmost if statement!! Instead, it should be after of the if statement like:

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   if{
       
   }
   return 0;
   

2. I did not use the + operator to sum the object of Sales class.

However, it runs quite well. ✔️

The implementation should be:

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#include <iostream>
#include "Sales_item.h"
​
using std::cout;
using std::cin;
using std::endl;
using std::cerr;
​
int main()
{
    cout << "Transaction program starts... You can fill the data now: " << endl;
    Sales_item total_item;
    if(cin >> total_item){
        int transaction_counts = 1;
        Sales_item processing_item;
        
        while(cin >> processing_item){
            if(total_item.isbn() == processing_item.isbn()){
                total_item+=processing_item;  //sum the record if ISBN is the same
            }else{
                cout << "The transaction record of " << total_item.isbn() << " is \n" << total_item << endl;
                total_item = processing_item;
                  }
        }
        cout << "The transaction record of " << total_item.isbn() << " is \n" << total_item << endl; //print the last value once out of while loop
    
    }else{
        cerr << "There is no transaction feeding in!" << endl;
        return -1;
    }
    
    return 0;
}
​

Console:

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Transaction program starts... You can fill the data now:
1-86092-042-X
10
15.00
1-86092-042-X
5
10.00
1-86092-004-7
20
5.00
The transaction record of 1-86092-042-X is
1-86092-042-X 15 200 13.3333
^Z
The transaction record of 1-86092-004-7 is
1-86092-004-7 20 100 5
​
Process returned 0 (0x0)   execution time : 32.923 s
Press any key to continue.

That is the end of this chapter. Keep coding!