how to display all elements in queue? - c

Question

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#define max 100
char name[max][80], data[80];
int front = 0;
int rear = 0;
int enqueue();
int dequeue();
int peek();
void display();
int main() {
int value;
int ch;
printf("------------------------------\n");
printf("\tMenu");
printf("\n------------------------------");
printf("\n [1] ENQUEUE");
printf("\n [2] DEQUEUE");
printf("\n [3] PEEK");
printf("\n [4] DISPLAY");
printf("\n------------------------------\n");
while(1)
{
printf("Choice : ");
scanf("%d", &ch);
switch(ch) {
case 1 : // insert
printf("\nEnter the Name : ");
scanf("%s",data);
value = enqueue(name, &rear, data);
if(value == -1 )
printf("\n QUEUE is Full \n");
else
printf("\n'%s' is inserted in QUEUE.\n\n",data);
break;
case 2 : // delete
value = dequeue(name, &front, &rear, data);
if( value == -1 )
printf("\n QUEUE is Empty \n");
else
printf("\n Deleted Name from QUEUE is : %s\n", data);
printf("\n");
break;
case 3:
value = peek(name, &front, &rear, data);
if(value != -1)
{
printf("\n The front is: %s\n", data);
}
break;
case 4:
display();
break;
case 5 : exit(0);
default: printf("Invalid Choice \n");
}
}
return 0;
}
int enqueue(char name[max][80], int *rear, const char data[80]) {
if(*rear + 1 == max)
return -1;
strcpy(name[*rear], data);
(*rear)++;
return 1;
}
int dequeue(char name[max][80], int *front, int *rear, char data[80])
{
if(*front == *rear)
return -1;
strcpy(data, name[(*front)++]);
return 1;
}
int peek(char name[max][80], int *front, int *rear, char data[80]) {
if(*front == *rear) {
printf(" QUEUE IS EMPTY\n");
return -1;
}
strcpy(data, name[*front]);
return 1;
}
void display(char name[max][80], int *front, int *rear, char data[80])
{
if(*front == -1 || *front > *rear)
{
printf("\n QUEUE IS EMPTY");
}
else
{
for(int i = *front; i<= *rear; i++)
{
printf("\t %s",data[i]);
}
}
}
Student here.
I need to display all elements inside the queue, but my program ends whenever I click option number 4, For example, the user inputs four names, "Jennie, Lisa, Jisoo, Rose", when the user selects option number 4, the program should print all 4 names. Even though I only input one name and need to print it, the program just ends. How to fix this?

Answer 1

I provided similar advise on earlier questions:
Your prototypes are incorrect (either fix them or delete them and move the definitions before use). I removed the prototype of display() and moved the implementation before use.
As your prototypes are wrong your compiler doesn't complain when you call dislay() without arguments (yours requires 4 arguments).
As display() doesn't change name, front, or rear I suggest you make first one const, and the other two integers. data is not used so eliminate it.
display(): queue is empty if front and rear have the same value.
Eliminate the global variables in favor of local variables in main().
Here is your working program:
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#define max 100
char name[max][80], data[80];
int front = 0;
int rear = 0;
int enqueue();
int dequeue();
int peek();
void display(const char name[max][80], int front, int rear) {
if(front == rear) {
printf("\n QUEUE IS EMPTY");
return;
}
for(int i = front; i < rear; i++)
{
printf("\t %s", name[i]);
}
printf("\n");
}
int main() {
int value;
int ch;
printf("------------------------------\n");
printf("\tMenu");
printf("\n------------------------------");
printf("\n [1] ENQUEUE");
printf("\n [2] DEQUEUE");
printf("\n [3] PEEK");
printf("\n [4] DISPLAY");
printf("\n------------------------------\n");
while(1)
{
printf("Choice : ");
scanf("%d", &ch);
switch(ch) {
case 1 : // insert
printf("\nEnter the Name : ");
scanf("%s",data);
value = enqueue(name, &rear, data);
if(value == -1 )
printf("\n QUEUE is Full \n");
else
printf("\n'%s' is inserted in QUEUE.\n\n",data);
break;
case 2 : // delete
value = dequeue(name, &front, &rear, data);
if( value == -1 )
printf("\n QUEUE is Empty \n");
else
printf("\n Deleted Name from QUEUE is : %s\n", data);
printf("\n");
break;
case 3:
value = peek(name, &front, &rear, data);
if(value != -1)
{
printf("\n The front is: %s\n", data);
}
break;
case 4:
display(name, front, rear);
break;
case 5 : exit(0);
default: printf("Invalid Choice \n");
}
}
return 0;
}
int enqueue(char name[max][80], int *rear, const char data[80]) {
if(*rear + 1 == max)
return -1;
strcpy(name[*rear], data);
(*rear)++;
return 1;
}
int dequeue(char name[max][80], int *front, int *rear, char data[80])
{
if(*front == *rear)
return -1;
strcpy(data, name[(*front)++]);
return 1;
}
int peek(char name[max][80], int *front, int *rear, char data[80]) {
if(*front == *rear) {
printf(" QUEUE IS EMPTY\n");
return -1;
}
strcpy(data, name[*front]);
return 1;
}
and sample session:
------------------------------
Menu
------------------------------
[1] ENQUEUE
[2] DEQUEUE
[3] PEEK
[4] DISPLAY
------------------------------
Choice : 1
Enter the Name : test
'test' is inserted in QUEUE.
Choice : 1
Enter the Name : test2
'test2' is inserted in QUEUE.
Choice : 4
test test2