stack

#include<stdio.h>
#include<stdlib.h>
int i=0,sta[100000];
void data_in(int z)
{
    if(i<0){
        printf("Stack is empty.\n");
        return;
    }
    else if(i==100000){
        printf("Stack is full.\n");
        return;
    }
    sta[i++]=z;
    return;
}
void data_out()
{
    if(i==0){
        printf("Stack is empty.\n");
        return;
    }
    printf("%d\n",sta[i-1]);
    sta[i--];
    return;
}
int last_data()
{
    if(i-1<0){
        printf("No data in stack.\n");
        return -1;
    }
    return sta[i-1];
}
int length()
{
    int k,nt=0;
    for(k=0;k<i;k++)nt++;
    return nt;
}
void display()
{
    int k;
    if(i==0){
        printf("No data.");
        return;
    }
    for(k=0;k<i;k++)printf("%d ",sta[k]);
    return;
}
int main()
{
    int a,x,q;
    printf("1.Push\n");
    printf("2.Pop\n");
    printf("3.Top\n");
    printf("4.Size\n");
    printf("5.Display\n");
    printf("6.Quit\n");
    while(1){
        scanf("%d",&x);
        switch(x)
        {
        case 1:
            scanf("%d",&a);
            data_in(a);
            break;
        case 2:
            data_out();
            break;
        case 3:
            q=last_data();
            if(q==-1)break;
            printf("%d\n",q);
            break;
        case 4:
            q=length();
            printf("%d\n",q);
            break;
        case 5:
            display();
            printf("\n");
            break;
        case 6:
            exit(1);
        }
    }
    return 0;
}