Printing of predefined phrases at random in C

Question

Hello, I’m a beginner in programming and I’m learning to code in C. I want to do a show that has some sentences already defined. Ex c/ vectors: char vet1[100] = {"Hello World!"}; char vet2[100] = {"segunda frase"}; ... and with each run, return a different phrase on the user screen. The closest I came was thinking about using the enum together with rand();, but it doesn’t work because it returns only a constant with decimal value. I think the solution would involve the use of several vetores ou uma matriz de strings, but I don’t know if that’s right.

Can anyone give me an idea? As long as it’s easy to understand for a beginner.

I have learned basic contents, and also vectors, matrices, functions, pointers, dynamic allocation and files.

NOTE: It is not necessary to pass the entire code, just explain me what is the best solution for implementing the sentence part.

Answer 1

First of all, as you already have the notion of vector, you know that placing multiple character vectors(strings) is tiring. So I advise using an array:

int main()
{
    char minhas_palavras[10][100];
    return 0;
}

With this, I can store 10 words of at most 100 characters each. It has a more efficient way, through pointers and dynamic memory allocation, but for this problem we do not need it.

To receive random numbers, you can use the Rand() function of the library and then play the first matrix input. For example:

int main()
{
    const int QUANTIDADE_PALAVRAS = 10;
    char minhas_palavras[QUANTIDADE_PALAVRAS][100];
    int numero_aleatorio;
    /* Aqui voce define suas palavras */
    numero_aleatorio = rand() % QUANTIDADE_PALAVRAS;
    printf("Palavra escolhida: %s", minhas_palavras[numero_aleatorio]);
    return 0;
}

Where we use a constant called QUANTIDADE_PALAVRAS which indicates that in this case the maximum value is 10 and does not vary.

If you want to use pointers and have a better memory utilization to not leave 87 characters empty in the case of "Hello World!". So the code below exemplifies this idea:

void grava_palavra(char *str, const char *palavra);
/* Pega todos os caracteres de *palavra e grava em *str
   assim como feito pela função strcopy */
char *aloca_memoria(int quantidade);
/* Essa funcao recebe um inteiro como argumento e retorna
   um ponteiro para caracter que indica onde foi alocada a memoria*/
int main()
{
    char *palavra;
    int quantidade_carac_palavra;
    /* Aqui voce define o tamanho da sua palavra. Ex: 13
       Não se esqueca do caracter '\0' no final     */
    palavra = aloca_memoria(quantidade_carac_palavra);
    grava_palavra(palavra, "Hello World!");
    printf("%s", palavra);
    free(palavra);
    return 0;
}

So in a similar way it works to place random numbers and get random phrases.

EDIT:

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

char *grava(const char *str)
{
    char *pont;
    int i, tamanho = 0;
    while(*(str+tamanho) != '\0') 
        tamanho++;
    pont = (char *)malloc((tamanho+1)*sizeof(char));
    for(i=0; i<tamanho+1; i++)
        *(pont+i) = *(str+i);
    return pont;
}
char **grava_matriz(int quantidade)
{
    return (char **) malloc(quantidade*sizeof(char*));
}

int main()
{
    char **mat;
    int ale, q = 2;
    mat = grava_matriz(q);
    *(mat) = grava("Hello");
    *(mat+1) = grava("hey");
    srand((unsigned)time(NULL));
    ale = rand()%q;
    printf("%s\n", *(mat+ale));
    free(*(mat));
    free(*(mat+1));
    free(mat);
    return 0;
}