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So, I'm totally new to C and I'm having some struggle with some basic concepts, mainly when it is about buffer, memory, and string creation. So, I have this assignment from College where I need to make an Array of Structs called Vehicles, and during the execution of the program I must take inputs from the user about the Vehicle mark, year, and licensePlate.

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

struct Vehicles {
    char mark[20];
    int modelYear;
    char licensePlate[8];
};

int main() {
    const int DEFAULT_SIZE = 10;
    struct Vehicles vehiclesArr[DEFAULT_SIZE];

    for(int i = 0; i < DEFAULT_SIZE ; i++) {
      memcpy(vehiclesArr[i].mark, "", 1);
      vehiclesArr[i].modelYear = 0;
      memcpy(vehiclesArr[i].licensePlate, "", 1);
    }

    int choice = 0;
    int counter = 0;

    printf("Hello Professor, my name is Henrique and in this program I will be your guide.\n");

    while (choice != 4) {        
        printf("So, what it will be for today?\n Choose a valid option.\n");   
        printf("0. Create a new Vehicle.\n");
        printf("1. List all saved vehicles.\n");       
        printf("2. Update a saved vehicle.\n");      
        printf("3. Delete a saved vehicle.\n");     
        printf("4. Quit Program.\n");       
        scanf("%d", &choice);       
      
        switch (choice) {   
            case 0:
              if (counter < 10) {
                printf("Choose a vehicle mark \n");
                scanf("%[^\n]s", vehiclesArr[counter].mark);
                printf("\n Choose the model year \n");
                scanf("%d", &vehiclesArr[counter].modelYear);
                printf("\n Choose license plate \n");
                scanf("%[^\n]s", vehiclesArr[counter].licensePlate);
                counter++;
                break;
              } else {
                printf("\n Storage limit reached.");
              }

            case 1: 
                for(int i = 0; i < DEFAULT_SIZE; i++) {
                  printf("\nModel: %s", vehiclesArr[i].mark);
                  printf("\nYear: %d", vehiclesArr[i].modelYear);
                  printf("\nLicense Plate: %s", vehiclesArr[i].licensePlate);
                }
                break;   

            case 2:     
                break;     

            case 3:     
                break;  

            case 4:         
                printf("Gently finishing program... Bye Bye!");     
                break;          
                
            default:        
                printf("\nWhat? The number must be between 0 and 4\n"); 
        } 
    } 
}

The problem is that, when I execute the program and press 0, the program just skip the user input on those two lines bellow:

...
    printf("Choose a vehicle mark \n");
    scanf("%[^\n]s", vehiclesArr[counter].mark);
...
    printf("\n Choose license plate \n");
    scanf("%[^\n]s", vehiclesArr[counter].licensePlate);
...

I'm trying to figure out what is happening been a while now, the only thing that works is if I use "%s", but I need the program to handle when user inputs an space character.

Can someone help me, and please explain why is this happening? This is my first question so I would appreciate if you guys also tell me how I can make my questions better.

Henrique Hefler
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  • This is canonical `scanf` problem #17a. Change `"%[^\n]s"` to `" %[^\n]"`. The extra `s` isn't causing a problem, but you need the extra space. – Steve Summit Sep 03 '21 at 03:02
  • It would have been simpler and safer to just use `%s` (at the cost of not being able to enter vehicle marks or license plates containing spaces). Whoever taught you about `%[]` really should have taught you the leading space trick. (Personally, I don't recommend using `%[]` at all.) – Steve Summit Sep 03 '21 at 03:04
  • Thanks for the answer, but why isn't recommended to use `%[]` ? – Henrique Hefler Sep 03 '21 at 04:15
  • @H.Hefler These are only my opinions, but: `scanf` has proved to be a very poor function, difficult to use correctly. Its only real use is to easily get data into the simple kinds of programs you write when you're just learning C — and for that use, it's only the very simple uses of `scanf` you need. But `%[]` is not a simple use — it's even harder to use correctly. So I believe you should use the simple `scanf` uses for your first few weeks, then [graduate to something better than `scanf`](https://stackoverflow.com/questions/58403537), and under that strategy you never end up using `%[]`. – Steve Summit Sep 03 '21 at 12:15

0 Answers0