Priority Scheduling with and without Aging

#include <stdio.h>
#define N 12
#define AF 25

struct process{
    char pid;
    int at;
    int et;
    int pri;
    int ct;
    int wt;
    int cwt;
    int tt;
}pro[N] =   {
                {'A', 0, 10, 5},
                {'B', 0, 3, 1},
                {'C', 2, 2, 3},
                {'D', 2, 1, 6},
                {'E', 2, 4, 3},
                {'F', 10, 5, 2},
                {'G', 10, 7, 3},
                {'H', 15, 8, 1},
                {'I', 20, 10, 2},
                {'J', 30, 9, 4},
                {'K', 40, 3, 5},
                {'L', 40, 2, 4}
            };
int done[N] = {0}, time = 0, sumWT = 0, sumTT = 0;
int calcNow(){
    int i, now;
    for(i = 0; i < N; i++) if(!done[i] && time >= pro[i].at){now = i; break;}
    for(; i < N; i++){
        if(done[i] || time < pro[i].at) continue;
        if(pro[i].pri < pro[now].pri) now = i;
        else if(pro[i].et == pro[now].et && pro[i].et < pro[now].et) now = i;
        else if((pro[i].et == pro[now].et) && (i < now)) now = i;
    }
    if(time < pro[now].at) return -1;
    return now;
}
void execute(int now){
    done[now] = 1;
    printf("%c executes from %d to %d\n", pro[now].pid, time, time+pro[now].et);
    pro[now].ct = time + pro[now].et;
    time = pro[now].ct;
    pro[now].wt = pro[now].ct - (pro[now].at + pro[now].et);
    pro[now].tt = pro[now].ct - pro[now].at;
    sumWT += pro[now].wt;
    sumTT += pro[now].tt;
}
void updatePriorities(){
    int i;
    for(i = 0; i < N; i++){
        if(!done[i] && time >= pro[i].at) pro[i].cwt = time - pro[i].at;
        if(pro[i].cwt >= 25 && pro[i].pri){
            pro[i].cwt = 0;
            pro[i].pri -= 1;
            printf("Priority of %c is now %d\n", pro[i].pid, pro[i].pri);
        }
    }
}
void printTable(){
    int i;
    printf("\tpid\tAT\tET\tPRI\tCT\tWT\tTT\n");
    for(i = 0; i < N; i++) printf("\t%c\t%d\t%d\t%d\t%d\t%d\t%d\n", pro[i].pid, pro[i].at, pro[i].et, pro[i].pri, pro[i].ct, pro[i].wt, pro[i].tt);
    printf("\nThe average waiting time is %.2f\nThe average turn around time is %.2f\n", sumWT/(float)N, sumTT/(float)N);
}
int main(){
    int i, now = 0;
    while(1){
        now = calcNow();
        if(now < 0){time++; continue;}
        execute(now);
        updatePriorities(); //commenting out this line gives Priority Scheduling without Aging
        for(i = 0; i < N; i++) if(!done[i]) break;
        if(i == N) break;
    }
    printTable();
    return 0;
}