A rubik's cube simulator. I wrote that during the IEEEXtreme 5.0 in 2011. The question can be found here: http://zaidpirwani.com/wp-content/uploads/downloads/2012/11/ieee-xtreme-6.0-faq-sample-questions.pdf

rubik.c

#include <string.h>

char u[3][3];
char l[3][3];
char f[3][3];
char r[3][3];
char b[3][3];
char d[3][3];
char temp[3];

void U()
{
    int i;
    
    for(i = 0; i < 3; i++)
        temp[i] = f[0][i];
    
    for(i = 0; i < 3; i++)
        f[0][i] = r[0][i];
    
    for(i = 0; i < 3; i++)
        r[0][i] = b[0][i];
    
    for(i = 0; i < 3; i++)
        b[0][i] = l[0][i];
    
    for(i = 0; i < 3; i++)
        l[0][i] = temp[i];
        
}

void L()
{
    int i;
    
    for(i = 0; i < 3; i++)
        temp[i] = f[i][0];
        
    for(i = 0; i < 3; i++)
        f[i][0] = u[0][2-i]; 
        
    for(i = 0; i < 3; i++)
        u[0][i] = b[i][2];
        
    for(i = 0; i < 3; i++)
        d[0][i] = b[2-i][2];
        
    for(i = 0; i < 3; i++)
        d[0][i] = f[i][0];
        
    for(i = 0; i < 3; i++)                
        d[0][i] = temp[i];
}

void F()
{
    int i;
    for(i = 0; i < 3; i++);
}

void R()
{
    int i;
    for(i = 0; i < 3; i++);
}

void B()
{
    int i;
    for(i = 0; i < 3; i++);
}

void D()
{
    int i;
    for(i = 0; i < 3; i++);
}

////////////////////////////////////////////////  MAIN FUNCTION  ///////////////////////////////////////////////

int main()
{
    int x;
    int y;
        
    int i;
    int j;
    
    char u0;
    char l0; 
    char f0;
    char r0; 
    char b0;
    char d0;
    
    scanf("%c", &u0);
    for(i = 0; i < 3; i++)
    {
        for(j = 0; j < 3; j++)
        {
            u[i][j] = u0;
        }
    }
    
    scanf("%c", &l0);        
    for(i = 0; i < 3; i++)
    {
        for(j = 0; j < 3; j++)
        {
            l[i][j] = l0;
        }
    }
    
    scanf("%c", &f0); 
    for(i = 0; i < 3; i++)
    {
        for(j = 0; j < 3; j++)
        {
            f[i][j] = f0;
        }
    }
    
    scanf("%c", &r0); 
    for(i = 0; i < 3; i++)
    {
        for(j = 0; j < 3; j++)
        {
            r[i][j] = r0;
        }
    }
    
    scanf("%c", &b0);   
    for(i = 0; i < 3; i++)
    {
        for(j = 0; j < 3; j++)
        {
            b[i][j] = b0;
        }
    }
    
    scanf("%c", &d0);
    for(i = 0; i < 3; i++)
    {
        for(j = 0; j < 3; j++)
        {
            d[i][j] = d0;
        }
    }
    
    char str[100];
    scanf("%s", &str);
    
    int k;
    char hist = 0;
    for(i = 0, j = 0; i < strlen(str) ; i++)
    {
        switch(str[i])
        {
            case 'U': U(); hist = str[i]; break; 
            case 'L': L(); hist = str[i]; break;
            case 'F': F(); hist = str[i]; break;
            case 'R': R(); hist = str[i]; break;
            case 'B': B(); hist = str[i]; break;
            case 'D': D(); hist = str[i]; break;
            default :                     break;
        }
            
        if( '1' <= str[i] && str[i] <= '9')
        {
            for(k = 0; k < str[i]-49; k++)
            {
                switch(hist)
                {
                    case 'U': U(); break; 
                    case 'L': L(); break;
                    case 'F': F(); break;
                    case 'R': R(); break;
                    case 'B': B(); break;
                    case 'D': D(); break;
                    default :      break;
                }
            }
        }
        if( str[i] == '\'')
        {
            for(k = 0; k < 2; k++)
            {
                switch(hist)
                {
                    case 'U': U(); break; 
                    case 'L': L(); break;
                    case 'F': F(); break;
                    case 'R': R(); break;
                    case 'B': B(); break;
                    case 'D': D(); break;
                    default :      break;
                }
            }
        }    
    }   
    
    for(x = 0; x < 3; x++)
    {
        for(y = 0; y < 3; y++)
        {
            printf("%c ", f[x][y]);
        }
        printf("\n");
    }
}