Lesson - 02

• Operators
• Conditionals
• Vectors
• Arrays
• Vectors
• StringStream
• Loops (while, for)

Write a program to detect if a birth date is important or not?

• 1 years - 18 years is Important
• 21 years is important
• 50 years is important
• greater than 65 is important

#include <iostream>

int main(int argc, const char **argv){
    // store the age
    int age = 0;

    // ask user for his age
    std::cout << "Enter your age: ";
    std::cin >> age;

    // store an important message.
    const std::string message = "Birthday is important.";

    // check for his age
    if(age >= 1 && age <=18){
        std::cout << message << std::endl;
    }
    else if((age == 21) || (age == 50)){
        std::cout << message << std::endl;
    }
    else if(age > 65){
        std::cout << message << std::endl;
    }
    else{
        std::cout << "Birthday is not important." << std::endl;
    }

    return 0;
}

Write a program that determine a grade or class a student would goto based on the conditions.

• Age = 5 : Go to kindergarten.
• Age 6 - 17 : Go to grade 1 - 12
• Age > 17 : Go to college

#include<iostream>

int main(int argc, const char **argv){
    // store the age
    int age = 0;

    // ask user for his age.
    std::cout << "Enter your age: ";
    std::cin >> age;

    // check for his age
    if(age < 5)
        std::cout << "Too young for school." << std::endl;
    else if(age == 5)
        std::cout << "Go to kindergarten." << std::endl;
    else if(age >= 6 && age <= 17)
        std::cout << "Go to grade " << age - 5 << std::endl;
    else
        std::cout << "Go to college." << std::endl;

    return 0;
}

Create an array with default value initialized to 1 for all elements.

#include <iostream>

int main(int argc, const char ** argv){
    // declare an array
    int nums[10] = {1, 1, 1, 1, 1, 1, 1, 1, 1, 1};

    // incorrect: results in {1, 0, 0, 0, 0, 0...}
    // int nums[10] = {1};

    // calculate length of array
    int len = sizeof(nums) / sizeof(nums[0]);

    // print the array
    for(int i=0; i<len; ++i){
        std::cout << "Nums : " << i << " = " << nums[i] << std::endl;
    }

    return 0;
}

Create an array that automatically infers its size.

#include <iostream>

int main(int argc, const char ** argv){

    // declare an array
    int nums[] = {10, 20, 30, 40, 50, 60};

    // calculate its length
    int len = sizeof(nums) / sizeof(nums[0]);

    // print elements of an array
    for(int i=0; i<len; ++i){
        std::cout << "Nums: " << i << " = " << nums[i] << std::endl;
    }

    return 0;
}

Create an array and perform following operations on it.

• Update its elements value
• Calculate its length using *(dereference) operator and sizeof function
• Create a multidimensional array
• Access elements of multidimensional array

#include <iostream>

int main(int argc, const char **argv){
    // create an array
    int nums[] = {10, 20, 30, 40, 50};

    // update element value of array
    nums[0] = 600;

    // calculate its length and print on screen
    int len = sizeof(nums) / sizeof(*nums);
    std::cout << "Length of nums array is : " << len << std::endl;

    // create a multidimensional array
    // read as 2 matrix of 2 rows and 3 columns each.
    int data[2][2][3] = {
        {
            {10, 20, 30},
            {40, 50, 60}
        },
        {
            {70, 80, 90},
            {100, 110, 120}
        }
    };

    // access elements of multidimensional array
    for(int matrix=0; matrix < 2; ++matrix){
        // to seperate multiple matrixes
        std::cout << "================" << std::endl;

        for(int row=0; row < 2; ++row){
            for(int col=0; col < 3; ++col){
                std::cout << data[matrix][row][col] << " ";
            }
            // to print like a matrix
            std::cout << '\n';
        }
        // to seperate multiple matrixes
        std::cout << "================" << std::endl;
    }

    return 0;
}

Create a vector to hold 2 elements and perform following operations

• Update value of elements
• Push an element at the end of vector to prove it is resizable
• Calculate size of a vector using method.
• Print the last index of vector using [len - 1] notation.

#include <iostream>
#include <vector>

int main(int argc, const char ** argv){

    // create a vector
    std::vector<int> nums(2);

    // update a vector
    nums[0] = 10;
    nums[1] = 20;

    // access elements of a vector
    std::cout << nums[0] << std::endl;

    // add extra element to a vector
    nums.push_back(30);

    // access size of a vector
    int len = nums.size()

    // print last index of a vector
    std::cout << "Last Index: " << nums[len -1 ] << std::endl;

    return 0;
}

Create a string and convert it into a vector

#include <iostream>
#include <string>
#include <sstream>

int main(int argc, const char ** argv){

    // create a string
    std::string sentence = "This is a collection of random words.";

    // create a vector to hold words
    std::vector<std::string> words;

    // create a string stream
    std::stringstream stream(sentence);

    // create a seperator
    char seperator = ' ';

    // create a variable to store a word temporary
    std::string tempWord = "";

    while(getline(stream, tempWord, seperator)){
        words.push_back(tempWord);
    }

    // print the vector elements
    for(int i=0; i < words.size; ++i){
        std::cout << words[i] << std::endl;
    }

    return 0;
}

Create a simple calculator to solve the calculation entered by user.

Sample Output:

• Enter calculation (ex. 20 + 3) : 40 + 4
• 40.0 + 4.0 = 44.0
• Program should support +, -, /, *
• Any unsupported operator should display an error.

#include <iostream>
#include <string>
#include <sstream>
#include <vector>

int main(int argc, const char ** argv){
    // store the user input
    std::string calculation = "0 + 0";

    // store the converted numbers in vector
    std::vector<std::string> splittedWords;

    // ask user for calculation
    std::cout << "Enter calculation (ex. 2 + 4) : ";
    std::getline(std::cin, calculation);

    // create a string stream to allow us to manipulate strings
    std::stringstream calcStream(calculation);

    std::string word = "";
    // split the numbers out of calculation
    while(getline(calcStream, word, ' ')){
        splittedWords.push_back(word);
    }

    // check the operand and store the result
    double result = 0;

    // convert the string into double numbers.
    double num1 = std::stod(splittedWords[0]);
    double num2 = std::stod(splittedWords[2]);

    std::string operand = splittedWords[1];

        if(operand == "+")
            result = num1 + num2;
        else if(operand == "-")
            result = num1 - num2;
        else if(operand == "*")
            result =  num1 * num2;
        else if(operand == "/")
            result = num1 / num2;
        else{
            // print the error and exit the program.
            std::cout << "Please enter only +, -, *, /" << std::endl;
            return 0;
        }

    // print the result
    std::cout << num1 << " " << operand << " " << num2 << " = " << result;

    return 0;
}