Remove spaces from string Using Queues: Cprogram

Write a program that compresses a string by deleting all space characters in the string. One way to do so is to use a queue of characters. Insert non space  characters from the string into the queue. When you reach the end of the string , dequeue the characters from the queue and place them back into the string.  

#include <stdio.h>

#define MAX 50

char q[MAX],f=-1,r=-1;

void enq(char val)

{

                if(r == MAX-1)

                                printf("queue is full and hence cannot insert");

                else if(f == -1 && r == -1)

                                f=r=0;

                else

                                r=r+1;

                q[r]=val;

}

char deq()

{

                char val;

                if(f == -1)

                                printf("queue is empty and hence cannot delete");

                else

                {

                                val = q[f];

                                if(f == r)

                                                f=r=-1;

                                else

                                                f=f+1;

                }

                return val;

}

int main()

{

                int i;

                char s[MAX];

                gets(s);

                for(i=0;s[i]!='\0';i++)

                {

                                if(s[i] != ' ')

                                                enq(s[i]);

                }

                for(i= f;i<=r;i++)

                                s[i]=deq();

                s[i]='\0';

                puts(s);

}

Output: