Differences Between C and C++

The following two programs, one written in C++ and the other written in C, both accept input from stdin that consists of the names of cars and the miles per gallon achieved by 3 drivers for those cars on a hypothetical test course. The programs print out the car with the best gas mileage. For example, given the input:

camry 23 17 28
g20 30 32 27
prius 48 38 41
f150 15 18 20
malibu 18 23 14

prius 42.3333

C++ Version

#include <iostream>
#include <string>

using namespace std;

// auto turns out to be a C++ reserved word so I substituted car instead
class car {
public:
  string name;
  float avg_mpg;
};

// it's better to declare constants rather than hard-coding them
const int NUM_DRIVERS = 3;

main() {
  car max_car;  // holds the car with the best gas mileage seen thus far
  float avg;    // average gas mileage for the current car
  int mpg[NUM_DRIVERS];  // gas mileage achieved by drivers for current car
  string model;   // name of current car

  // initialize max_car.avg_mpg to a small value or else it might never get set
  max_car.avg_mpg = -1.0; 
  while (cin >> model >> mpg[0] >> mpg[1] >> mpg[2]) {
    // remember to cast either the numerator or divisor to a float in order
    // to avoid integer arithmetic
    avg = (mpg[0] + mpg[1] + mpg[2]) / (float)NUM_DRIVERS;
    if (avg > max_car.avg_mpg) {
      max_car.name = model;
      max_car.avg_mpg = avg;
    }
  }
  cout << "best car = "
       << max_car.name
       << endl;
  cout << "mpg = " 
       << max_car.avg_mpg
       << endl;
}

C Version

// the header files are different in C
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

// auto turns out to be a C reserved word so I substituted car instead
struct car {  // C uses structs rather than classes
  char name[100];  // C represents strings using char arrays

  float avg_mpg;
};


// it's better to declare constants rather than hard-coding them but you
// may have to use #define rather than const 
#define NUM_DRIVERS 3

main() {
  
  struct car max_car;  // holds the car with the best gas mileage seen thus far
  
  float avg;    // average gas mileage for the current car
  int mpg[NUM_DRIVERS];  // gas mileage achieved by drivers for current car
  
  char model[100];   // name of current car
  

  // initialize max_car.avg_mpg to a small value or else it might never get set
  max_car.avg_mpg = -1.0; 
  
  // must use scanf rather than cin to read from stdin
  while (scanf("%s %d %d %d", model, &mpg[0], &mpg[1], &mpg[2]) != EOF) {
  
    // remember to cast either the numerator or divisor to a float in order
    // to avoid integer arithmetic
    avg = (mpg[0] + mpg[1] + mpg[2]) / (float)NUM_DRIVERS;
    if (avg > max_car.avg_mpg) {
      
      // need to use strcpy rather than assignment operator (=) to assign
      // strings from one variable to another
      strcpy(max_car.name, model);
      
      max_car.avg_mpg = avg;
    }
  }
  
  // use printf rather than cout to print to stdout
  printf("best car = %s\n", max_car.name);
  printf("mpg = %f\n", max_car.avg_mpg);
  
}