Trying to sort a struct array in Descending Order - c

Question

To preface what I'm trying to do - I'm trying to make a Shortest Job First (SJF), the OS algo in C.
And to handle the sort-by-burst-time, I'm pushing all the ready processes in a stack, and then sorting that stack in a descending order. So for example - if the stack looks like 3,5,1,2 with "2" on top, I'm trying to sort it as: 5,3,2,1 with "1" on top. So when I start using pop, I'll get elements in the order I require.
But the problem with the code I'm going to show is, it orders 1,1,5,3 as 5,1,1,3. The last process "3" is never sorted.
Code for Sorting:
void sortByBurst() {
int size = top;
struct fcfs temp;
for (int i = 0; i < size - 1; i++) {
for (int j = 0; j < (size - 1 - i); j++) {
if (stack[j].burst < stack[j + 1].burst) {
temp = stack[j];
stack[j] = stack[j + 1];
stack[j + 1] = temp;
}
}
}
}
And in case you want to see where I'm handling the rest of the logic i.e making decisions on what to push - this is the for loop for that:
for (i = 0; i < numOfProc; i++) {
if (first_process == 1 && p[i].arrival <= current_time && p[i].completed == 0) {
min_index = i;
} else if (first_process == 0 && last_index != -1) {
for (int k = 0; k < numOfProc; k++) {
if (p[k].completed == 0 && p[k].arrival <= p[last_index].max_slot && p[k].inQ != 1) {
push(p[k]);
p[k].inQ = 1;
critical_case = 1;
} else if (p[k].completed == 0 && p[k].arrival > finalp[last_index].max_slot && p[k].inQ != 1) {
min_index = k;
}
}
if (critical_case == 1) {
sortByBurst();
struct fcfs compare = pop();
for (int l = 0; l < numOfProc; l++) {
if (compare.pid == p[l].pid) {
min_index = l;
break;
}
}
}
break;
}
}
The input I'm testing my code with is:
1. Process 1 | 2 (Arrival) | 1 (Burst)
2. Process 2 | 1 (Arrival) | 5 (Burst)
3. Process 3 | 4 (Arrival) | 1 (Burst)
4. Process 4 | 0 (Arrival) | 6 (Burst)
5. Process 5 | 2 (Arrival) | 3 (Burst)
Required Output:
1. Process 4 | 0 (Arrival) | 6 (Burst)
2. Process 1 | 2 (Arrival) | 1 (Burst)
3. Process 3 | 4 (Arrival) | 1 (Burst)
4. Process 5 | 2 (Arrival) | 3 (Burst)
5. Process 2 | 1 (Arrival) | 5 (Burst)
Output I'm Getting:
1. Process 4 | 0 (Arrival) | 6 (Burst)
2. Process 5 | 2 (Arrival) | 3 (Burst)
3. Process 3 | 4 (Arrival) | 1 (Burst)
4. Process 1 | 2 (Arrival) | 1 (Burst)
5. Process 2 | 1 (Arrival) | 5 (Burst)
As you can see, the Process 5 should be at 4th place in the list. But because in Stack - it's still on Top even after sorting, the algo is not working as it should. Kindly look into what I'm doing wrong here.
Complete Code:
#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
struct fcfs {
int pid, arrival, burst, min_slot, max_slot, wait_time, completed, inQ;
};
struct fcfs stack[10];
int top = -1;
void push(struct fcfs process);
struct fcfs pop();
void sortByBurst();
void pline(int x);
void main() {
int i, numOfProc, j;
int counter = 0;
int current_time = 0;
int completed = 0;
struct fcfs p[10], finalp[10];
int first_process = 1;
int prevMaxSlot = 0;
int last_index = -1;
int critical_case = 0;
printf("Enter total number of Processes \n");
scanf("%d", &numOfProc);
for (i = 0; i < numOfProc; i++) {
printf("Enter Arrival Time & Burst Time for Process %d: \n", i + 1);
scanf("%d %d", &p[i].arrival, &p[i].burst);
p[i].pid = i + 1;
p[i].wait_time = 0;
p[i].completed = 0;
p[i].inQ = 0;
}
int prev = 0;
while (completed != numOfProc) {
int min_index = -1;
for (i = 0; i < numOfProc; i++) {
if (first_process == 1 && p[i].arrival <= current_time && p[i].completed == 0) {
min_index = i;
} else if (first_process == 0 && last_index != -1) {
for (int k = 0; k < numOfProc; k++) {
if (p[k].completed == 0 && p[k].arrival <= p[last_index].max_slot && p[k].inQ != 1) {
push(p[k]);
p[k].inQ = 1;
critical_case = 1;
} else if (p[k].completed == 0 && p[k].arrival > finalp[last_index].max_slot && p[k].inQ != 1) {
min_index = k;
}
}
if (critical_case == 1) {
sortByBurst();
struct fcfs compare = pop();
for (int l = 0; l < numOfProc; l++) {
if (compare.pid == p[l].pid) {
min_index = l;
break;
}
}
}
break;
}
}
if (min_index == -1) {
current_time++;
} else {
if (p[min_index].arrival == prevMaxSlot) {
p[min_index].min_slot = prevMaxSlot;
p[min_index].max_slot = p[min_index].arrival + p[min_index].burst;
} else if (p[min_index].arrival < prevMaxSlot || p[min_index].arrival == prevMaxSlot) {
p[min_index].min_slot = prevMaxSlot;
p[min_index].max_slot = p[min_index].min_slot + p[min_index].burst;
} else if (p[min_index].arrival > prevMaxSlot) {
p[min_index].min_slot = p[min_index].arrival;
p[min_index].max_slot = p[min_index].arrival + p[min_index].burst;
}
p[min_index].wait_time = (first_process == 1) ? 0 : abs(p[i].min_slot - prev);
p[min_index].completed = 1;
prev = current_time;
prevMaxSlot = p[min_index].max_slot;
finalp[counter++] = p[min_index];
first_process = 0;
last_index = min_index;
completed++;
}
}
pline(44);
printf("Slot\tPID\tArrival\t\tBurst\n");
pline(44);
for (i = 0; i < numOfProc; i++) {
if ((finalp[i].min_slot - finalp[i - 1].max_slot) > 0 && i > 0) {
printf("%d - %d\tNONE\tNONE\t\tNONE\n", finalp[i - 1].max_slot, finalp[i].min_slot);
} else if ((abs(0 - finalp[i].min_slot) > 0 && i == 0)) {
printf("0 - %d\tNONE\tNONE\t\tNONE\n", finalp[i].min_slot);
}
printf("%d - %d\t%d\t%d\t\t%d\n", finalp[i].min_slot, finalp[i].max_slot, finalp[i].pid, finalp[i].arrival,
finalp[i].burst);
}
pline(44);
}
void pline(int x) {
for (int i = 0; i < x; i++) {
printf("-");
}
printf("\n");
}
void push(struct fcfs process) {
if (top == 10)
printf("\n Overflow");
else {
top = top + 1;
stack[top] = process;
}
}
struct fcfs pop() {
struct fcfs process;
if (top == -1)
printf("Underflow");
else {
process = stack[top];
top = top - 1;
}
return process;
}
void sortByBurst() {
int size = top + 1;
struct fcfs temp;
for (int i = 1; i < size - 1; i++) {
for (int j = 0; j < (size - 1 - i); j++) {
if (stack[j].burst < stack[j + 1].burst) {
temp = stack[j];
stack[j] = stack[j + 1];
stack[j + 1] = temp;
}
}
}
}

Answer 1

The issue was with top & i = 1;
In the sorting function, int size = top + 1 and initializing the for loop with i = 0 fixed it.
Thanks a lot to all who contributed.