Practice Problems

Let’s look at some practice problems on std::vector, structs, and references.

1. Let’s modify our struct Planet example to add the period as a member and fill the period automatically via Kepler’s law in a loop.

   solution

   Listing 43 period.cpp

   #include <iostream>
   #include <vector>
   #include <cmath>
   #include <format>
   #include <string>
   
   struct Planet {
       std::string name;
       double a{};            // semi-major axis
       double e{};            // eccentricity
       double P{};
   };
   
   int main() {
   
       std::vector<Planet> planets{{.name="Mercury", .a=0.3871, .e=0.2056},
                                   {.name="Venus",   .a=0.7233, .e=0.0068},
                                   {.name="Earth",   .a=1.0000, .e=0.0167},
                                   {.name="Mars",    .a=1.5237, .e=0.0934},
                                   {.name="Jupiter", .a=5.2029, .e=0.0484},
                                   {.name="Saturn",  .a=9.5370, .e=0.0539},
                                   {.name="Uranus",  .a=19.189, .e=0.0473},
                                   {.name="Neptune", .a=30.070, .e=0.0086}};
   
       for (auto &p : planets) {
           p.P = std::sqrt(std::pow(p.a, 3.0));
       }
   
       for (auto p : planets) {
           std::cout << std::format("planet {} has a period of {:.2f} years.\n",
                                    p.name, p.P);
       }
   }
   

2. Create a vector with this list of names:

   luke
   leia
   han
   chewy
   obi-wan
   yoda
   vader
   lando
   

   Now loop over the names and use the std::toupper() function from cctype to capitalize the first letter in each name (updating the vector.

   Finally loop over the vector again and output the names.

   solution

   Listing 44 names.cpp

   #include <iostream>
   #include <string>
   #include <vector>
   #include <cctype>
   
   int main() {
   
       std::vector<std::string> names{"luke",
                                      "leia",
                                      "han",
                                      "chewy",
                                      "obi-wan",
                                      "yoda",
                                      "vader",
                                      "lando"};
   
       for (auto &nm : names) {
           nm[0] = std::toupper(nm[0]);
       }
   
   
       for (const auto &nm : names) {
           std::cout << nm << std::endl;
       }
   
   }
   

3. Create a vector containing the numbers 0 through 9.

   Now loop over the vector, and modify each element to be the sum of itself and the all the previous elements.

   There are several ways to do this. For this example, we will create a variable called previous that will be updated in the loop body to always hold the previous sum.

   Upon completion, output the new values to the screen.

   solution

   Listing 45 sum.cpp

   #include <iostream>
   #include <vector>
   #include <format>
   
   int main() {
   
       std::vector<int> nums{0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
   
       int previous{};
       for (auto &n : nums) {
           n += previous;
           previous = n;
       }
   
       int i{};
       for (auto n : nums) {
           std::cout << std::format("{:2} : {:3}\n", i, n);
           i++;
       }
   
   }