问解密一个4位数字

EN

new_num1 = (old_num1 + 7) % 10;
new_num2 = (old_num2 + 7) % 10;
new_num3 = (old_num3 + 7) % 10;
new_num4 = (old_num4 + 7) % 10;

#include <stdio.h>

int main()
{
    int codice;
    int num1, num2, num3, num4, temp1, temp2, new_num1_temp, new_num2_temp;

    printf("\n(LOLCrytter v0.1)\n\nInsert 4-digit code to crypt: -1 to exit ");
    scanf("%d", &codice);    

    if(codice == -1)
        return 0;

    while(codice < 1000 || codice > 9999) {
        printf("\nInsert NUMERIC (!) 4-digit code bru..: ");
        scanf("%d", &codice); 
    }

    // Get every digit by logic math and not by strings functions      
    temp1 = codice;
    num1 = temp1 / 1000;
    temp2 = temp1 % 1000;
    num2 = temp2 / 100;
    temp1 = temp2 % 100;
    num3 = temp1 / 10;
    num4 = temp1 % 10;

    // Crypting...    
    num1 = (num1 + 7) % 10;
    num2 = (num2 + 7) % 10;
    num3 = (num3 + 7) % 10;
    num4 = (num4 + 7) % 10;

    // Crypting...    
    new_num1_temp = num3;
    num3 = num1;
    num1 = new_num1_temp;   
    new_num2_temp = num4;
    num4 = num2;
    num2 = new_num2_temp;

    printf("\nNew code: %d%d%d%d\n\n", num1, num2, num3, num4);

    return 0;
}