c replace dot with comma in a float number

Question

I'm developing a simple GTK+3 program that do simple calculation.
I have a problem with floating point number because if i write . instead of , the total will be wrong.
So I have float price; and i want to replace . with , .
Example: user write 100.60 as price and i want to convert it into 100,60 . How can i do it?
I've thought to strchr but it is a float and i think i cannot use it xD
Thanks :)

EDIT: added the code

#include <gtk/gtk.h>
#include <stdlib.h>
#include <string.h>

GtkWidget *window;
GtkWidget *grid;
GtkWidget *c_button;
GtkWidget *q_button;
GtkWidget *u_name;
GtkWidget *h_name;
GtkWidget *pass;
GtkWidget *label_user;
GtkWidget *label_host;
GtkWidget *label_pass;

/* Funzione attivata alla pressione del pulsante connect */
int calcolo_guadagno(void){
    int num_btp, i, len;
    float prezzo_attuale, subtotale, totale, diff_prezzo_attuale, PREZZO_PARTENZA = 99.42;
    char cmcd[15];
    num_btp = (atoi(gtk_entry_get_text(GTK_ENTRY(h_name)))/PREZZO_PARTENZA);
    prezzo_attuale = atof(gtk_entry_get_text(GTK_ENTRY(u_name)));
    diff_prezzo_attuale = (prezzo_attuale - PREZZO_PARTENZA);
    subtotale = (num_btp * diff_prezzo_attuale);
    totale = subtotale-((subtotale/100)*12.5);
    if(prezzo_attuale < PREZZO_PARTENZA){
        strcpy(cmcd, "Sei in perdita...");
        gtk_entry_set_text(GTK_ENTRY(pass),cmcd);
        return EXIT_SUCCESS;
    }
    if(prezzo_attuale == PREZZO_PARTENZA){
        strcpy(cmcd, "Sei in pari...");
        gtk_entry_set_text(GTK_ENTRY(pass),cmcd);
        return EXIT_SUCCESS;
    }
    sprintf(cmcd, "%.3f", totale);
    gtk_entry_set_text(GTK_ENTRY(pass),cmcd);
    return EXIT_SUCCESS;
}



   int main (int argc, char *argv[]){

    /* Inizializziamo le librerie GTK+ */
    gtk_init (&argc, &argv);

    /* Creiamo la finestra principale, impostiamo il titolo, la posizione e la dimensione */
    window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
    gtk_window_set_title (GTK_WINDOW (window), "Calcolo Guadagno BTP");
    gtk_window_set_position (GTK_WINDOW(window), GTK_WIN_POS_CENTER);
    gtk_window_set_default_size (GTK_WINDOW(window), 350, 250);

    /* Quando premiamo chiudi si 'disturgge' tutto */
    g_signal_connect (window, "destroy", G_CALLBACK (gtk_main_quit), NULL);

    /* Impostiamo il bordo e dichiariamo le finestra ridimensionabile */
    gtk_container_set_border_width (GTK_CONTAINER (window), 10);
    gtk_window_set_resizable(GTK_WINDOW(window), TRUE);

    /* Creiamo una nuova griglia, la aggiungiamo alla finestra e impostiamo gli spazi fra i vari widget */
    grid = gtk_grid_new ();
    gtk_container_add (GTK_CONTAINER (window), grid);
    gtk_grid_set_row_spacing (GTK_GRID (grid), 3);

    /* Creiamo delle label con il relativo nome */
    label_user = gtk_label_new("Prezzo attuale ");
    label_host = gtk_label_new("Soldi investiti ");
    label_pass = gtk_label_new("Guadagno netto ");

    /* Creo una entry_text */
    h_name = gtk_entry_new();
    /* Impostiamo il testo trasparente che scompare quando clicco o scrivo */
    gtk_entry_set_placeholder_text (GTK_ENTRY (h_name), "Soldi investiti");
    u_name = gtk_entry_new();
    gtk_entry_set_placeholder_text (GTK_ENTRY (u_name), "Prezzo attuale");
    pass = gtk_entry_new();
    /* Impostiamo il campo password non visibile */
    gtk_editable_set_editable (GTK_EDITABLE (pass), 0);
    /* Creiamo i pulsanti e li connettiamo alle relative funzioni */
    c_button = gtk_button_new_with_label ("Calcola");
    g_signal_connect (c_button, "clicked", G_CALLBACK (calcolo_guadagno), NULL);
    q_button = gtk_button_new_with_label ("Esci");
    g_signal_connect (q_button, "clicked", G_CALLBACK (gtk_main_quit), NULL);

    /* Imposto i widget come espandibili sia in orizzontale che in verticale */
    gtk_widget_set_hexpand(u_name, TRUE);
    gtk_widget_set_vexpand(u_name, TRUE);
    gtk_widget_set_hexpand(h_name, TRUE);
    gtk_widget_set_vexpand(h_name, TRUE);
    gtk_widget_set_hexpand(pass, TRUE);
    gtk_widget_set_vexpand(pass, TRUE);

    /* Posizioniamo i widget all'interno della griglia */
    gtk_grid_attach (GTK_GRID (grid), label_host, 0, 0, 1, 1);
    gtk_grid_attach (GTK_GRID (grid), h_name, 1, 0, 1, 1);
    gtk_grid_attach (GTK_GRID (grid), label_user, 0, 1, 1, 1);
    gtk_grid_attach (GTK_GRID (grid), u_name, 1, 1, 2, 1);
    gtk_grid_attach (GTK_GRID (grid), label_pass, 0, 2, 1, 1);
    gtk_grid_attach (GTK_GRID (grid), pass, 1, 2, 1, 1);
    gtk_grid_attach (GTK_GRID (grid), c_button, 0, 3, 2, 1);
    gtk_grid_attach (GTK_GRID (grid), q_button, 0, 4, 2, 1);

    /* Mostriamo tutti i widget */
    gtk_widget_show_all (window);

    /* Entriamo nel loop principale delle GTK+, da questo punto  l'applicazione attende l'accadere di un qualsiasi evento */
    gtk_main ();

    return 0;
}

Answer 1

Having prices as floats is in general a very bad idea. floating-point arithmetic is imprecise and will come back to bite you in very weird situations. Use a struct to represent both parts of the currency and then implement some arithmetic and printing with them.

type struct {
  int main;
  int sub;
} money;

void add(money* result, money* x, money* y);

void print(money* x);
void read(money* result, const char* input);

Your print function can explicitly specify what separator should be used.

Answer 2

Have a look at setlocale .

If you are using a locale that uses comma as seperator, it will be used in input/output operations.

Is that what you are looking for?

Answer 3

The strpbrk function in <string.h> can help.

void dot_to_comma(char *input) {
    char *ptr = NULL;
    while(ptr = strpbrk(input, ".")) { //find the first dot in input
        *ptr = ','; //replace the dot with a comma
    }
}

Answer 4

int i;
int len = strlen(string);
for (i = 0; i < len; i++) {
    if (string[i] == '.') {
        string[i] = ',';
        i = len; // or `break;`
    }
}