请检查我的代码的编程质量

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

int main(){
    char command[50]; // массив для ввода комманды
    char* time_start;                                                               
    time_t t = time(NULL);                                                        
    time_start = ctime(&t);               

    printf("************************   Welcome to danyOS   *************************\n");
    
    while (1 == 1){
        printf("~user$ ");
        scanf("%s", command);
        if ((command[0] == 't') &&(command[1] == 'e') && (command[2] == 's') && (command[3] == 't')){
            printf("System is OK\n");
        }
        else if ((command[0] == 'd') &&(command[1] == 'a') && (command[2] == 't') && (command[3] == 'e') && (command[4] == 't') && (command[5] == 'i') && (command[6] == 'm') && (command[7] == 'e')){                                       
            t = time(NULL);
            time_start = ctime(&t);                                                                     
            printf("%s", time_start);       
        }
        /*
        else if((command[0] == "N") && (command[1] == "I") && (command[2] == "P")){ // работа с NIP
            printf("package NIP readding...\n");

            FILE *nip_file;
            nip_file = fopen("NIP.txt","r");            
            scanf("%s", command);
            if ()
        }
        */
        else if((command[0] == 'c') &&(command[1] == 'a') && (command[2] == 'l') && (command[3] == 'c')){
            long long int number1 = 0;
            long long int number2 = 0;
            char calc_command[1];
            printf("Input first number: ");
            scanf("%d", &number1);
            printf("Input second number:");
            scanf("%d", &number2);
            printf("Input command (+, -, /, *): ");
            scanf("%s", calc_command);
            if (calc_command[0] == '+'){
                printf("Result = %d\n", number1 + number2);
            }
            else if (calc_command[0] == '-'){
                printf("Result = %d\n", number1 - number2);
            }
            else if (calc_command[0] == '*'){
                printf("Result = %d\n", number1 * number2);
            }
            else if (calc_command[0] == '/'){
                printf("Result = %d\n", number1 / number2);
            }   
            else{
                printf("Wrong command!\n");
            }   
        }
        else if((command[0] == 't') &&(command[1] == 'i') && (command[2] == 'm') && (command[3] == 'e') && (command[4] == 'r')){
            int timer_time = 0;
            printf("Timer successfully!\n");
            printf("Input time in minutes: ");
            scanf("%d", &timer_time);
            timer_time = timer_time * 60;       
            printf("To continue, press any key\n");
            getchar();
            getchar();  
            printf("Timer start!\n");           
            for (int i = 0; i < timer_time; i++){                                               
                timer_time = timer_time - 1;
                printf("Timer: %d\n",timer_time);
                sleep(1);
            }
            printf("\nTime is up!\n");
        }                                    
        else{
            printf("No such command!\n");
        }       
    }   
    return 0;
}