ncurses displaying word at the center and make it into uppecase and lowercase

Question

#include <ncurses.h>
#include <unistd.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
int main(int argc, char *argv[]){
    int x,y,ch;
    if(argc != 2){
        fprintf(stderr,"there is no value to be show\n");
        exit(1);
    }
    getmaxyx(stdscr,y,x);
    
    initscr();
    start_color();
    init_pair(COLOR_RED, COLOR_RED, COLOR_BLACK);  
    init_pair(COLOR_GREEN, COLOR_GREEN, COLOR_BLACK);
    init_pair(COLOR_WHITE,COLOR_WHITE, COLOR_BLACK);
    keypad(stdscr,TRUE);
    
    crmode();
    
    noecho();
    while(ch != 'q'){
        mvprintw(y/2, x/2, "%s", argv[1]); 
        refresh();
        ch = getch();
        if(ch == 'u'){
            attron(COLOR_PAIR(COLOR_GREEN));
            mvprintw(y/2, x/2, "%s", strupr(argv[1]));
        }
        else if(ch == 'l'){
            attron(COLOR_PAIR(COLOR_RED));
            mvprintw(y/2, x/2, "%s", argv[1]);
        }
        else if(ch == 'o'){
            attron(COLOR_PAIR(COLOR_WHITE));
            mvprintw(y/2, x/2, "%s", argv[1]); 
        }
        else{
            continue;
        }
    }
    endwin();
    return 0;
}

So from this code I want to display string argv[1] at the center of the terminal. When the user press u I want to make it uppercase when the user press l I want to make it into the lowercase. At my code when I want to make the word into the uppercase I want to use strupr to make it into uppercase but cannot compile this code properly. It said implicit declaration for the strupr function.

And I think for putting into the center of the terminal I already make the proper program by using mvprintw(y/2,x/2) but despite of the word displayed at the center it displayed at the top left of the terminal. Is there somebody know where my mistake at?

Answer 1

You can't query getmaxyx until after you have initialized the screen with initscr. Or, better said, you can do the query but you won't get meaningful information.

strupr is not a standard C function, and I guess your C library doesn't implement it. You can implement it by looping over the string calling toupper:

char* my_strupr(char* str) {
  for (unsigned char* p = (unsigned char*)str; *p; ++p) {
    *p = toupper(*p);
  }
  return str;
}

That's not the best way of converting to upper case. It won't work if you have any non-ascii characters in your input. There are libraries which provide Unicode-aware string transformations, and you should think about using one of them. (Also, you might want to use the wide-char-enable ncurses. See the manual for details.)