Comparaison else if/switch

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

#define ITERATION_COUNT 10000000

int ReadString(char* str, int arraySize);

int main()
{
    /*
    ** Pour éviter au compilateur d'être trop sauvage sur les optimisations
    ** et de donner un temps d'exécution nul, on prend une variable donnée par l'utilisateur.
    */

    char str[50];
    char c;
    int i, iteration, length;
    clock_t t1_1, t1_2;
    clock_t t2_1, t2_2;

    printf("Entrez une chaine (50 caracteres max): ");
    length = ReadString(str, 50);
    fflush(stdin); /* Vade retro Léonidas */

    /* L'algorithme ici est débile, il transforme une lettre en une autre, rien de plus */

    /* if/else if */
    t1_1 = clock();
    for (iteration = 0; iteration < ITERATION_COUNT; ++iteration)
    {
        for (i = 0; i < length; ++i)
        {
            if (str[i] == 'a')
                c = 'p';
            else if (str[i] == 'b')
                c = 'o';
            else if (str[i] == 'c')
                c = 'i';
            else if (str[i] == 'd')
                c = 'u';
            else if (str[i] == 'e')
                c = 'y';
            else if (str[i] == 'f')
                c = 't';
            else if (str[i] == 'g')
                c = 'r';
            else if (str[i] == 'h')
                c = 'e';
            else if (str[i] == 'i')
                c = 'z';
            else if (str[i] == 'j')
                c = 'a';
            else if (str[i] == 'k')
                c = 'm';
            else if (str[i] == 'l')
                c = 'l';
            else if (str[i] == 'm')
                c = 'k';
            else if (str[i] == 'n')
                c = 'j';
            else if (str[i] == 'o')
                c = 'h';
            else if (str[i] == 'p')
                c = 'g';
            else if (str[i] == 'q')
                c = 'f';
            else if (str[i] == 'r')
                c = 'd';
            else if (str[i] == 's')
                c = 's';
            else if (str[i] == 't')
                c = 'q';
            else if (str[i] == 'u')
                c = 'n';
            else if (str[i] == 'v')
                c = 'b';
            else if (str[i] == 'w')
                c = 'v';
            else if (str[i] == 'x')
                c = 'c';
            else if (str[i] == 'y')
                c = 'x';
            else if (str[i] == 'z')
                c = 'w';
            else
                c = '?';

            str[i] = c;
        }
    }
    t1_2 = clock();

    /* switch */
    t2_1 = clock();
    for (iteration = 0; iteration < ITERATION_COUNT; ++iteration)
    {
        for (i = 0; i < length; ++i)
        {
            switch (str[i])
            {
                case 'a':
                    c = 'p';
                    break;

                case 'b':
                    c = 'o';
                    break;

                case 'c':
                    c = 'i';
                    break;

                case 'd':
                    c = 'u';
                    break;

                case 'e':
                    c = 'y';
                    break;

                case 'f':
                    c = 't';
                    break;

                case 'g':
                    c = 'r';
                    break;

                case 'h':
                    c = 'e';
                    break;

                case 'i':
                    c = 'z';
                    break;

                case 'j':
                    c = 'a';
                    break;

                case 'k':
                    c = 'm';
                    break;

                case 'l':
                    c = 'l';
                    break;

                case 'm':
                    c = 'k';
                    break;

                case 'n':
                    c = 'j';
                    break;

                case 'o':
                    c = 'h';
                    break;

                case 'p':
                    c = 'g';
                    break;

                case 'q':
                    c = 'f';
                    break;

                case 'r':
                    c = 'd';
                    break;

                case 's':
                    c = 's';
                    break;

                case 't':
                    c = 'q';
                    break;

                case 'u':
                    c = 'n';
                    break;

                case 'v':
                    c = 'b';
                    break;

                case 'w':
                    c = 'v';
                    break;

                case 'x':
                    c = 'c';
                    break;

                case 'y':
                    c = 'x';
                    break;

                case 'z':
                    c = 'w';
                    break;

                default:
                    c = '?';
                    break;
            }
        }
    }

    t2_2 = clock();

    printf("Version \"else if\": %g\n", ((float) (t1_2-t1_1)) / CLOCKS_PER_SEC);
    printf("Version switch   : %g\n", ((float) (t2_2-t2_1)) / CLOCKS_PER_SEC);

    getchar(); /* Une attente si CodeBlocks n'est pas bien réglé */
    return 0;
}

int ReadString(char* str, int arraySize)
{
    int c;
    int i;
    int maxLength = arraySize-1;
    char* ptr = str;

    fflush(stdin); /* El diablo */
    for (i = 0; i < maxLength; ++i)
    {
        c = getchar();
        if (c == '\n' || c == EOF)
            break;

        *ptr++ = (char) c;
    }

    *ptr = '\0';

    return i;
}