Question

So, this is probably a bit huge, and probably messy and incorrect (it’s really beginner). I’m just learning C, and part of the work I’m required to do involves switching this program to a C++ program. The main thing I need to do is replace all structs with classes, and have all of the functions used in the code be class functions (members? If I recall…)

I have a pretty good grasp on a lot of basics, but the concept is to just sort of “modify” the code. I don’t see how to “modify” my previous work by just switching to classes. As is, I feel like the program needs to pretty much be re-written to use classes. Maybe I’m missing the simplicity here. I don’t want someone to do the work for me, I just want to know if there’s a simple way to format my structs to work as classes.

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

//Struct for friend array pointers.
typedef struct friendstruct{
        char *firstname;
        char *lastname;
        char *homephone;
        char *cellphone;
} frnd;
//Buffer for use in storing in the main program.
typedef struct bufferstruct{
        char firstname[20];
        char lastname[20];
        char homephone[20];
        char cellphone[20];
} frndbuff;
//Add friend function.
void addfriend(frnd friendarray[], frndbuff newfrnd, int count, int opened){
     friendarray[count].firstname = malloc(sizeof(newfrnd.firstname));  //Assign memory before copying string.
     friendarray[count].lastname = malloc(sizeof(newfrnd.lastname));
     friendarray[count].homephone = malloc(sizeof(newfrnd.homephone));
     friendarray[count].cellphone = malloc(sizeof(newfrnd.cellphone));
     strcpy(friendarray[count].firstname, newfrnd.firstname);
     //printf("%s", friendarray[count].firstname);
     //printf("%s", newfrnd.firstname);
     strcpy(friendarray[count].lastname, newfrnd.lastname);
     strcpy(friendarray[count].homephone, newfrnd.homephone);
     strcpy(friendarray[count].cellphone, newfrnd.cellphone);
     //friendarray[count].lastname = newfrnd.lastname;
     //friendarray[count].homephone = newfrnd.homephone;
     //friendarray[count].cellphone = newfrnd.cellphone;

     if(opened==0){
     printf("\nA new friend has been added to the phonebook.");
     }
}
//Deleteing friends.
int deletefriend(frnd friendarray[], frndbuff newfrnd, int count){
     int n = 0;
     int success = 0;
     while(n<count){
           if(strcmp(newfrnd.lastname,friendarray[n].lastname)==0){ //Comparing strings.
                 while(n<count-1){
                                 strcpy(friendarray[n].firstname, friendarray[n+1].firstname);
                                 strcpy(friendarray[n].lastname, friendarray[n+1].lastname);
                                 strcpy(friendarray[n].homephone, friendarray[n+1].homephone);//Removes previously used position.
                                 strcpy(friendarray[n].cellphone, friendarray[n+1].cellphone);
                                 //friendarray[n].lastname = friendarray[n+1].lastname;
                                 //friendarray[n].homephone = friendarray[n+1].homephone;
                                 //friendarray[n].cellphone = friendarray[n+1].cellphone;
                                 n++;
                 }
           success = 1;
           count = count - 1;
           break;
           }
           n++;
     }      
           if(success==1){
           printf("\nThe entry for %s has been removed from the phonebook.", newfrnd.lastname);
           }else{
           printf("\nThat entry was not found");
           }
           //printf("%i", count);
return count;
}
//Show friend by last namme. Identical to delete friend, without removal.
void showfriend(frnd friendarray[], frndbuff newfrnd, int count){
     int n = 0;
     int success = 0;
     while(n<count){
           if(strcmp(newfrnd.lastname, friendarray[n].lastname)==0){
           printf("\n\n%s %s %s (home) %s (cell)\n", friendarray[n].firstname, friendarray[n].lastname, friendarray[n].homephone, friendarray[n].cellphone);                      
           success = 1;
           break;
           }
     n++;
     }

           if(success==0){
           printf("\nThat entry was not found");
           }
}
//DIsplays entire phonebook.
void phonebook(frnd friendarray[], int count){
     int n = 0;
     //printf("%i", count); Used in debugging.
     while(n<count){
     printf("\n%s %s %s (home) %s (cell)\n", friendarray[n].firstname, friendarray[n].lastname, friendarray[n].homephone, friendarray[n].cellphone);
     n++;
     }
}
//Find friend based on last name.
void searchfriend(frnd friendarray[], frndbuff newfrnd, int count){
     int n = 0;
     int success = 0;
     while(n<count){
           if(strcmp(newfrnd.lastname, friendarray[n].lastname)==0){
           printf("\n\n%s %s %s (home) %s (cell)\n", friendarray[n].firstname, friendarray[n].lastname, friendarray[n].homephone, friendarray[n].cellphone); 
           success = 1;                     
           }
     n++;
     }

           if(success==0){
           printf("\nThat entry was not found");
           }
}                        

int main(){
    int option, option2;
    frndbuff currentfriend;
    frnd friendarray[50];
    int count = 0;
    int filecount = 0;
    int opened = 0;
    //Phonebook load previous to main loop.
    printf("\nDo you have a previously saved phonebook you'd like to load?\n1) Yes\n2) No\n");
    printf("\nChoose an option : ");
    scanf("%i", &option2);
        if(option2==1){

                  FILE *fileopen;
                  fileopen = fopen("phonebook.dat", "r"); //File open for reading.
                  if (fileopen != NULL){
                               filecount = 0;
                               opened = 1;
                               printf("\nYour previous phonebook has been loaded : ");
                               while(fscanf(fileopen, "%s %s %s (home) %s (work)\n",&currentfriend.firstname, &currentfriend.lastname, &currentfriend.homephone, &currentfriend.cellphone)==4){
                                                      printf("\n%s %s %s (home) %s (work)\n",currentfriend.firstname, currentfriend.lastname, currentfriend.homephone, currentfriend.cellphone);
                                                      addfriend(friendarray, currentfriend, filecount, opened);
                                                      filecount++;
                               }
                               count = filecount;
                  }else if(fileopen == NULL){
                               printf("\nA previous phonebook could not be found.");
                  }
    }

while(1==1){



    opened = 0;                
    printf("\n\nPhone Book Application\n1) Add Friend\n2) Delete Friend\n3) Show a Friend\n4) Show phone book\n5) Search by last name\n6) Quit\n");    
    printf("\n\nWhat option would you like to choose : ");
    scanf("%i", &option);  
    //Option ensuring.
    if(option<1 || option>6){
                printf("\nYou did not enter a valid option, please try again.");
                option = 6;
    }

    if(option==1){
                  printf("\nFirst Name : ");
                  scanf("%s", &currentfriend.firstname);
                  printf("\nLast Name : ");
                  scanf("%s", &currentfriend.lastname);
                  printf("\nHome Phone : ");
                  scanf("%s", &currentfriend.homephone);
                  printf("\nCell Phone : ");
                  scanf("%s", &currentfriend.cellphone);
                  //printf("%s", currentfriend.firstname); Debugging.
                  addfriend(friendarray, currentfriend, count, opened);


                  count++;
                  //printf("%i", count); Debugging.
                  //All options call the previously made functions and pass the buffer.
    }else if(option==2){
                  printf("\nEnter the last name of the friend you'd like to delete : ");
                  scanf("%s", &currentfriend.lastname);
                  count = deletefriend(friendarray, currentfriend, count);
    }else if(option==3){
                  printf("\nEnter the last name of the friend you'd like to view : ");
                  scanf("%s", &currentfriend.lastname);
                  showfriend(friendarray, currentfriend, count);
    }else if(option==4){
                  phonebook(friendarray, count);
    }else if(option==5){
                  printf("\nEnter the last name you'd like to search : ");
                  scanf("%s", &currentfriend.lastname);
                  searchfriend(friendarray, currentfriend, count);
    }else if(option==6){
                  option2 = 0;
                  printf("\nWould you like to save your phonebook to a file?\n1) Yes\n2) No");
                  printf("\n Choose an option : ");
                  scanf("%i", &option2);
                  if(option2==1){
                                 filecount = 0;
                                 FILE *filesave;
                                 filesave = fopen("phonebook.dat", "w"); //File open for writing.
                                 while(filecount<count){
                                 //File written in the same method it is read.
                                 fprintf(filesave, "%s %s %s (home) %s (work)\n",friendarray[filecount].firstname, friendarray[filecount].lastname, friendarray[filecount].homephone, friendarray[filecount].cellphone);
                                 filecount++;
                                 }
                  }
                  printf("\nThank you for using this Phone Book Application!");
                  break;
    }
}
//Files closed.
fclose(fileopen);
fclose(filesave);
getch();
return 0;
} 

Answer 1

The main difference with C++ is to use std::string instead of the raw character arrays. Then you don’t use malloc and free. You just let std::string take responsibility for the memory management.

Similarly, you’d use a std::vector for the storage of the friends.

You could also replace the i/o with C++ iostreams i/o, which is simpler and safer.

Bjarne Stroustrup wrote a little introductory article showing how to transform a little C program into C++ (“Learning Standard C++ as a New Language”, C/C++ Users Journal pp 43-54 May 1999).

You will just have to “unlearn” some C ways of doing things, and adopt more C++’ish ways. 🙂