Mã lệnh:

#include <stdio.h>
#include <conio.h>

int main(){
    int pwd;
    printf("Nhap mat khau: ");
    scanf("%d",&pwd);
    if (pwd == 1234)
        printf("Dang nhap thanh cong");
    else
        printf("Dang nhap that bai");
    getch();
    return 0;
}