This shows how to grab the rows and columns of your terminal using either the TIOCGSIZE or TIOCGWINSZ ioctls. NB: There's no error handling and no fallback case. Tested on Debian and OS-X.

ioctl-term-info.c

#include <stdio.h>
#include <unistd.h>

#include <sys/ioctl.h>

struct term_info {
    int rows;
    int cols;
};

struct term_info
GetTermInfo(){
    struct term_info info = {-1, -1};

#ifdef TIOCGSIZE
        struct ttysize ts;
        ioctl(STDIN_FILENO, TIOCGSIZE, &ts);
        info.cols = ts.ts_cols;
        info.rows = ts.ts_lines;
#elif defined(TIOCGWINSZ)
        struct winsize ts;
        ioctl(STDIN_FILENO, TIOCGWINSZ, &ts);
        info.cols = ts.ws_col;
        info.rows = ts.ws_row;
#endif /* TIOCGSIZE */

    return info;
}

int main(int argc, char **argv){
    struct term_info ti = GetTermInfo();
    printf("Rows: %d, Cols: %d\n", ti.rows, ti.cols);
    return 0;
}