#include <stdio.h>
#include <string.h>

int replace(char str[51], char oldchar, char newchar, int i, int check);
int epigrafi(char str[51], int sum3, int i, int apantisi, int z);

int main()
{
    int epilogi;
    char str[51];
    printf("Eishgage mia alfarithmitiki seira ews 50 xarakthres: \n");
    fgets(str, sizeof(str), stdin);

epiloges:
    printf("\nDialexe mia apo tis parakato epiloges");
    printf("\n1.Psakse ena xarakthra mesa se mia alfarithmitiki seira");
    printf("\n2.Antikatastash xarakthra");
    printf("\n3.Elenxos seiras gia karkiniki epigrafh");
    printf("\n4.Eksodos apo to programma");
    printf("\nEpilogi: ");
ksana:
    scanf("%d", &epilogi);

    if (epilogi == 1)
    {
        int i, sum = 0;
        char key;
        printf("Dwse mou gramma gia anazitisi: ");
        scanf(" %c", &key);
        for (i = 0; i < 51; i++)
        {
            if (str[i] == key)
                sum += 1;
        }
        if (sum == 0)
            printf("\nTo gramma den briskete stin seira");
        else if (sum == 1)
            printf("\nTo gramma brethike stin seira");
        else
            printf("\nTo gramma vrethike %d fores", sum);

        goto epiloges;
    }
    else if (epilogi == 2)
    {
        int check = 0, i = 0;
        char oldchar, newchar;
        printf("Dwse xarakthra pros antikatastash: \n");
        scanf(" %c", &oldchar);
        printf("Dwse ton xarakthra pou thes na ton antikatasthseis \n");
        scanf(" %c", &newchar);
        check = replace(str, oldchar, newchar, i, check);
        printf("H nea seira einai: %s", str);

        if (check > 0)
            printf("\nO xarakthras brethike sthn seira kai antikatastithike %d fores \n", check);
        else
            printf("O xarakthras pou edwses den vrethike sthn seira \n");

        goto epiloges;
    }
    else if (epilogi == 3)
    {
        int apantisi = 0, z = 0, i = 0, sum3 = 0;
        apantisi = epigrafi(str, i, z, sum3, apantisi);
        if (apantisi == 1)
            printf("\nH epigrafh einai karkiniki\n");
        else if (apantisi == 0)
            printf("\nH epigrafh den einai karkiniki\n");

        goto epiloges;
    }
    else if (epilogi == 4)
    {
        return 0;
    }
    else if (epilogi > 4 || epilogi < 1)
    {
        printf("H epilogh pou edwses den einai swsth ksanaprospathise: ");
        goto ksana;
    }
}

int replace(char str[51], char oldchar, char newchar, int i, int check)
{
    for (i = 0; i < 51; i++)
    {
        if (str[i] == oldchar)
        {
            str[i] = newchar;
            check++;
        }
    }
    return check;
}

int epigrafi(char str[51], int sum3, int i, int z, int apantisi)
{
    int length = ((strlen(str) - 1));
    printf("%d", length);
    for (i = 0; i <= length; i++)
    {
        for (z = length; z > 0; z--)
        {
            if (str[i] == str[z])
            {
                (sum3 = sum3 + 1);
            }
        }
    }
    if (sum3 == length)
    {
        apantisi = 1;
    }
    return apantisi;
}