How can I sort names by gender in C?

This is a 15-element array of type char:

char n[15];

And here you write in said vector:

for(i=0;i<e;i++){
    scanf("%s",&n[i]);

Problems of these three lines? Two, basically:

1. You overwrite user data

   As I have commented, nit is a vector of 15 elements of type char:

         00 01 02 03 04 05 06 07 08 09 10 11 12 13 14
    n -> xx xx xx xx xx xx xx xx xx xx xx xx xx xx xx
   

   So, on the first iteration you store a string starting at the position given by n[0]:

         00 01 02 03 04 05 06 07 08 09 10 11 12 13 14
    n ->  D  a  v  i  d \0 xx xx xx xx xx xx xx xx xx
   

   On the second iteration, you store another string starting at the position of n[1]:

         00 01 02 03 04 05 06 07 08 09 10 11 12 13 14
    n ->  D  L  a  u  r  a \0 xx xx xx xx xx xx xx xx
   

   And, as you can see, that causes the first chain to be lost.

2. buffer overflow

   Continuing with what was said in the previous point, when eyou have high values, the algorithm will start writing in the last positions of the array, then there will be less useful space to store the strings, which increases the risk that the code writes outside the array limits. For example, if we are in the 12th iteration, we can only enter a string of 2 characters:

         00 01 02 03 04 05 06 07 08 09 10 11 12 13 14
    n -> xx xx xx xx xx xx xx xx xx xx xx xx  A  B \0
   

   If we introduce a larger string we end up writing outside the limits of the array:

         00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 ~~~~~~~~~ <-- desbordamiento
    n -> xx xx xx xx xx xx xx xx xx xx xx xx  R  u  b  e  n  \0
   

   When this happens two things can happen:

   • The Operating System detects that you access memory that does not belong to you and kills your process
   • You overwrite the value of other variables, which makes your program (or other processes) unstable

To solve these problems you have to use a double array or matrix

// Puede almacenar 15 nombres, cada uno con una longitud máxima de 19 caracteres
char n[15][20];

You don't really need to use arrays in n. If you keep reading you will see why.

Although of course, it may nnot be the most appropriate name for a variable... they will not charge you any extra, so I suggest that the names of the variables be representative:

char nombre[15][20];

Your code will be more readable and it will be more difficult for you to screw up when using variables.

Once you have already requested the name and gender, copy the data to another array (depending on the gender):

if(g[i]=='m'){  
  n[i]=h[i];
  c=c+1;
}

This code also has two problems:

1. The assignments are done just the other way around, that is, right now you are copying characters from h into nand it should be the other way around. Also, note that you are copying characters, not strings.

   An important detail in C is that strings are copied using functions, like strcpy. If this function gives you errors it is probably because you are not trying to copy strings but, as in this case, single characters (the compiler can be your friend)

   As I mentioned before, you don't need to use arrays in n. The reason is that your code just asks for a name and copies it to another list based on gender.

   That is, the final lists must be arrays, but itn can be a string of characters to use:

    // Cadena de caracteres
    char nombre[20];
   
    // Listas de cadenas
    char hombres[15][20];
    char mujeres[15][20];
   

   In this way, you reuse nombresto request the data from the user:

    for(i=0;i<e;i++){
        printf("ingrese el nombre %d\n",i+1);
        scanf("%s", nombre);
   
        strcpy(hombres[i], nombre);
   

2. For the array hyou should use the index cinstead ofi

   Effectively, you use cand pin what looks like it should be the indices for the two genre lists... but you don't take advantage of their values ​​when populating those lists.

Applying the fixes:

int main( ) {
  char nombre[20];
  char genero[15];
  char hombres[15][20];
  char mujeres[15][20];

  int indice_hombres = 0;
  int indice_mujeres = 0;

  int total_datos;
  printf("\nCuantos nombre desea ingresar?\n");
  scanf("%d",&total_datos);

  for(int i=0;i<total_datos;i++)
  {
    printf("ingrese el nombre %d\n",i+1);
    scanf("%s", nombre);
    printf("escoja el genero de %s\n", nombre);
    scanf("%s", genero);

    if(genero[0] == 'm')
    {  
      strcpy(hombres[indice_hombres], nombre);
      indice_hombres++;
    }
    else if( genero[0] == 'f')
    {
      strcpy(mujeres[indice_mujeres], nombre);
      indice_mujeres++;
    }
  }

The problem you are seeing corresponds to this line:

printf("escoja el genero de %s\n",n[i]);

This is because you are indicating that you are going to print a string (%s) however you give the function a char (n[i]).

                          string   char
                            V       V
printf("escoja el genero de %s\n",n[i]);

C interprets a string as an array of chars terminated by the end-of-string character corresponding to '\0'. If your compiler didn't stop you, the program would start reading consequent memory locations an[i] looking for '\0'until it would eventually hit a memory space that isn't reserved for it and you would get a segmentation fault or similar error as a result.

You can check this by replacing the line with:

printf("escoja el genero de %c\n",n[i]);

And you will see how the error is corrected because the printf function knows that it should only print one character.

Now this is where the problem comes in because you're actually wanting to save an entire string and not just one character. However, in your definition:

char n[15],h[15],d[15], g[15];

You are creating 4 arrays of 15 characters, in other words 4 strings. In array n you have 15 spaces for just 1 character.

A solution to this would be to create a 2-dimensional array, that is, an array of X number of strings of Y characters. And it would be declared like this:

char nombres[MAX_CANT_NOMBRES][MAX_TAMANO_NOMBRE+1];

This would create a list of size MAX_CANT_NOMBRESnames of size MAX_TAMANO_NOMBRE. The +1 is to make room for the end of string character '\0'.

Here I leave you an example so you can see how it would work, ignore the function imprimirLista, I made it just so you could see the result of the list that is created and add more advanced and confusing concepts.

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

int MAX_TAMANO_NOMBRE = 20;    //Máximo largo de un nombre
int MAX_CANT_NOMBRES =15;      //Cuántos nombres vamos a guardar como máximo


void imprimirLista(char (*nombres)[MAX_CANT_NOMBRES][MAX_TAMANO_NOMBRE+1], char (*generos)[MAX_CANT_NOMBRES][2], int cantidad){
    for(int i=0;i<cantidad;i++){    
        printf("Nombre#%d: %s, sexo:%s\n", cantidad,(*nombres)[i],(*generos)[i]);

    }
}

int main( ) {
    char nombres[MAX_CANT_NOMBRES][MAX_TAMANO_NOMBRE+1]; //15 nombres de un tamaño de 20 caracteres cada uno (se agrega uno para el caracter de fin de string '\0')
    char generos[MAX_CANT_NOMBRES][2];//Tienen un tamaño de 2 porque es la letra +'\0'
    int iteraciones = 0;
    
    printf("\nCuantos nombres desea ingresar?\n");
    scanf("%d",&iteraciones);
    
    for(int i=0;i<iteraciones;i++){
        printf("Ingrese el nombre %d\n",i+1);
        scanf("%s",nombres[i]);
        printf("Escoja el genero de %s (digite m o f)\n",nombres[i]);
        scanf("%s",generos[i]);
    }
    
    imprimirLista(&nombres,&generos,iteraciones);
  
}

For a simpler reading we can parameterize with #definethe sizes of the 2D array and use typedefsomething like this for the structures:

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

#define MAX_TAMANO_NOMBRE 20    //Máximo largo de un nombre
#define MAX_CANT_NOMBRES  15    //Cuántos nombres vamos a guardar como máximo

//Definimos un datatype que consiste en una lista de 15 nombres, con 20 caracteres (Array 2D de chars)
//El 20+1 es para incluir el caracter de fin de string: '\0'
typedef char listaNombres [MAX_CANT_NOMBRES][MAX_TAMANO_NOMBRE+1];

//Definimos un datatype que consiste en una lista de 15 nombres, con 20 caracteres (Array 2D de chars)
//El 20+1 es para incluir el caracter de fin de string: '\0'
typedef char listaGeneros [MAX_CANT_NOMBRES][2];

void imprimirLista(listaNombres * nombres, listaGeneros * generos, int cantidad){
    for(int i=0;i<cantidad;i++){    
        printf("Nombre#%d: %s, sexo:%s\n", cantidad,(*nombres)[i],(*generos)[i]);

    }
}


int main( ) {
    listaNombres nombres;
    listaGeneros generos;
    
    int iteraciones = 0;
    
    printf("\nCuantos nombres desea ingresar?\n");
    scanf("%d",&iteraciones);
    
    for(int i=0;i<iteraciones;i++){
        printf("Ingrese el nombre %d\n",i+1);
        scanf("%s",nombres[i]);
        printf("Escoja el genero de %s (digite m o f)\n",nombres[i]);
        scanf("%s",generos[i]);
    }
    
    imprimirLista(&nombres,&generos,iteraciones);
    
}

I hope this doesn't raise more questions than answers, however it will pull you in the right direction, C is a language with a very steep learning curve.

Good luck in your programming!

The problem is that your array ndoes not have enough capacity for what it collects scanf(), the strings themselves are character strings (arrays):

char cadena[] = {"h","o","l","a"};

When you do scanf("%s",&n[i]);this you are telling the compiler to store in the first element of the array n(the first iteration) the input string. You are entering a string into a space where only one character can enter.

The solution to this is to create an array of arrays, where the arrays are the strings:

char n[15][15];

For this reason, it is also advisable to define the arrays in the same way hand dthat they must have the same capacity as n, this is because they will eventually store an element of n.

Another thing I noticed, is that you do assignments like this:

n[i] = h[i];

This is not valid in the first instance, since the assignment must be done from left to right, not the other way around, because at that moment that index his empty.

It can also generate errors, it is dangerous. It is always better to make use of strcpy(), defined in the header <string.h>:

strcpy(h[i],n[i]);

In short, the arrays must be defined like this:

char n[15][15];
char g[15]; //'g' solo va a recibir una letra
char h[15][15];
char d[15][15];

and the first loop forshould look like this:

for (i = 0;i < e;i = i + 1) {
    printf("ingrese el nombre %d\n",i + 1);
    scanf("%s",&n[i]);
    printf("escoja el genero de %s\n",n[i]);
    scanf("%s",&g[i]);

    if(g[i] == 'm') {  
        strcpy(h[i],n[i]);
        c = c + 1;
    } else if(g[i] == 'f') {
        strcpy(d[i],n[i]);
        p = p + 1;    
    }
}

I hope I have served you, greetings.