How to position the input text cursor in C?

If you are under some Unix terminal (xterm, gnome-terminal …), you can use console codes:

#include <stdio.h>

#define clear() printf("\033[H\033[J")
#define gotoxy(x,y) printf("\033[%d;%dH", (y), (x))

int main(void)
{
    int number;

    clear();
    printf(
        "Enter your number in the box below\n"
        "+-----------------+\n"
        "|                 |\n"
        "+-----------------+\n"
    );
    gotoxy(2, 3);
    scanf("%d", &number);
    return 0;
}

Or using Box-drawing characters:

printf(
    "Enter your number in the box below\n"
    "╔═════════════════╗\n"
    "║                 ║\n"
    "╚═════════════════╝\n"
);

More info:

man console_codes