* What is a bad program?

* What is a good program?

* What are good programming practices?

* Are there programming languages that make it easy to write good programs?

* What is your previous experience with C?

* What are the advantages of C as a programming language?

* What are the disadvantages of C? What about C++?

* What is a data-structure?

* Which data structures do you know in C?

* Can you write a "hello, world" in C?

#include <stdio.h>

int main() {
  printf("Oi, Mundo!\n");
  return 0;
}

* When was the C programming language designed and implemented?

* What about C++?

* Can you write a "hello, world" in C++?

#include <iostream>

int main() {
  std::cout << "Oi, Mundo!\n";
  return 0;
}

* What are the main differences between the two programs?

* And what are the differences that you think exist between C and C++?

* How can we use strings in C?

#include <stdio.h>

int main() {
  char s0[4] = {'d', 'c', 'c', '\0'};
  char s1[] = "dcc";
  printf("%s\n", s0);
  printf("%s\n", s1);
}

* How can we know the size of a string in C?

#include <stdio.h>
#include <string.h>

unsigned size(char* s) {
  unsigned i = 0;
  while (s[i] != '\0')
    i++;
  return i;
}

int main() {
  char s0[] = "abc";
  char *s1 = "wxyz";
  printf("Last char s0 = %u\n", size(s0));
  printf("Last char s1 = %u\n", size(s1));
  printf("Last char s0 = %lu\n", strlen(s0));
}

* Can you modify a string constant in C?

#include <stdio.h>
  
int main() {
  char s0[] = "abcde";
  char *s1 = "vwxyz";
  printf("s0 = %s, s1 = %s\n", s0, s1);
  s0[0] = '_';
  printf("s0 = %s, s1 = %s\n", s0, s1);
  s1[0] = '_';
  printf("s0 = %s, s1 = %s\n", s0, s1);
}

Read: https://stackoverflow.com/questions/4208444/c-difference-between-and

"s0[] declares an array of characters, which is filled with abcde. *s1 is a
 pointer to a string constant."

* How can we use the string class in C++?

#include <iostream>
#include <string>

using namespace std;

int main () {

   string str1 = "Hello";
   string str2 = "World";
   string str3;
   int  len ;

   // copy str1 into str3
   str3 = str1;
   cout << "str3 : " << str3 << endl;

   // concatenates str1 and str2
   str3 = str1 + str2;
   cout << "str1 + str2 : " << str3 << endl;

   // total length of str3 after concatenation
   len = str3.size();
   cout << "str3.size() :  " << len << endl;

   return 0;
}

* Can we modify strings?

#include <iostream>
#include <string>

using namespace std;

int main () {
   string str = "oi";

   str[0] = 'e';
   printf("%d\n", str[0]);
   return 0;
}

* What if they are marked as constants?

#include <iostream>

using namespace std;

int main () {
   const string str = "oi";

   str[0] = 'e';
   printf("%d\n", str[0]);
   return 0;
}

* What will be printed below?

#include <iostream>

using namespace std;

int main() {
  string s0 = "oi";
  string s1 = s0;
  s0[0] = 'a';
  cout << s1 << endl;
}

* What are typical operations that we can perform on strings?

#include<iostream>
#include<string>

using namespace std; 

int main() { 
  // Declaring string 
  string str; 

  // Taking string input using getline() 
  // "geeksforgeek" in givin output 
  getline(cin,str); 

  // Displaying string 
  cout << "The initial string is : "; 
  cout << str << endl; 

  // Using push_back() to insert a character at end 
  str.push_back('s'); 

  // Displaying string 
  cout << "The string after push_back operation is : "; 
  cout << str << endl; 

  // Using pop_back() to delete the character at the end 
  str.pop_back(); 

  // Displaying string 
  cout << "The string after pop_back operation is : "; 
  cout << str << endl; 

  return 0; 
}

* What do you think is the meaning of the syntax o.m()?

* How can we iterate over the characters in a string?

#include<iostream> 
#include<string> 
using namespace std; 
int main()  {
  string str = "DCC204"; 

  for (auto c: str) {
    cout << c << endl;
  } 

  return 0; 
}

* What if we need to iterate on the inverse order?

#include<iostream> 
#include<string> 
using namespace std; 
int main()  {
  string str = "DCC204"; 

  for (auto i = str.rbegin(); i != str.rend(); ++i) {
    cout << *i << endl;
  } 

  return 0; 
}

* How to convert a C++ string to a C style char array?

#include <stdio.h>
#include <string>

using namespace std; 
  
int main() { 
    string s = "DCC204";
    int n = s.length(); 
    char char_array[n + 1]; 
    strcpy(char_array, s.c_str()); 
    printf("%s\n", char_array);
    return 0; 
}

* How to read a file with pairs of numbers? E.g.:

$> cat file.txt
3 4
1 5
1 3
2 5
4 5

#include <fstream>
#include <stdio.h>

int main(int argc, char** argv) {
  std::ifstream infile(argv[1]);
  int a, b;
  while (infile >> a >> b) {
    printf("(%d, %d)\n", a, b);
  }
}

* What are the problems with this program?

* What happens if we do not pass a file name in the input?

* How to fix this program?

#include <iostream>
#include <fstream>
#include <stdio.h>

int main(int argc, char** argv) {
  std::ifstream infile(argv[1]);
  if (!infile.is_open()) {
    std::cerr << "Failed to open file\n";
  }
  int a, b;
  while (infile >> a >> b) {
    printf("(%d, %d)\n", a, b);
  }
}

* Can't you test if the argument is missing and report it back to the user?

#include <iostream>
#include <fstream>
#include <stdio.h>

int main(int argc, char** argv) {
  if (argc != 2) {
    std::cerr << "Syntax: cmd <file_name>\n";
    return 1;
  } else {
    std::ifstream infile(argv[1]);
    if (!infile.is_open()) {
      std::cerr << "Failed to open file\n";
      return 2;
    }
    int a, b;
    while (infile >> a >> b) {
      printf("(%d, %d)\n", a, b);
    }
  }
  return 0;
}

* How can you check the output of an executable file in Linux?

$> ./a.out file.txt
$> echo $?

* How can you save the points in a struct?

#include <iostream>
#include <fstream>
#include <stdio.h>

struct Point {
  int x;
  int y;
};

int main(int argc, char** argv) {
  if (argc != 2) {
    std::cerr << "Syntax: cmd <file_name>\n";
    return 1;
  } else {
    std::ifstream infile(argv[1]);
    if (!infile.is_open()) {
      std::cerr << "Failed to open file\n";
      return 2;
    }
    struct Point p;
    while (infile >> p.x >> p.y) {
      printf("(%d, %d)\n", p.x, p.y);
    }
  }
  return 0;
}

* Can you save the points in a data-structure, e.g., a list of points?

#include <iostream>
#include <fstream>
#include <stdio.h>
#include <vector>

struct Point {
  int x;
  int y;
};

int main(int argc, char** argv) {
  if (argc != 2) {
    std::cerr << "Syntax: cmd <file_name>\n";
    return 1;
  } else {
    std::vector<struct Point> vec;
    std::ifstream infile(argv[1]);
    if (!infile.is_open()) {
      std::cerr << "Failed to open file\n";
      return 2;
    }
    struct Point p0;
    while (infile >> p0.x >> p0.y) {
      vec.push_back(p0);
    }
    for (auto p1: vec) {
      printf("(%d, %d)\n", p1.x, p1.y);
    }
  }
  return 0;
}

* What are the advantages of vectors over arrays?

* Why we get this warning when we compile the program? E.g.:

$> clang++ centroid2.cpp 
centroid2.cpp:26:10: warning: 'auto' type specifier is a C++11 extension

* How to avoid it?

$> clang++ -std=c++11 centroid2.cpp

* How to find the centroid of the points?

#include <iostream>
#include <fstream>
#include <stdio.h>
#include <vector>

struct Point {
  int x;
  int y;
};

int main(int argc, char** argv) {
  if (argc != 2) {
    std::cerr << "Syntax: cmd <file_name>\n";
    return 1;
  } else {
    std::vector<struct Point> vec;
    std::ifstream infile(argv[1]);
    if (!infile.is_open()) {
      std::cerr << "Failed to open file\n";
      return 2;
    }
    struct Point p0;
    while (infile >> p0.x >> p0.y) {
      vec.push_back(p0);
    }
    // Find the centroid:
    double center_x = 0.0;
    double center_y = 0.0;
    for (auto p1: vec) {
      center_x += p1.x;
      center_y += p1.y;
    }
    double size = vec.size();
    printf("(%.3lf, %.3lf)\n", center_x/size, center_y/size);
  }
  return 0;
}

* Why are there so few data-structures in C?