hash table program that will take the first character of a string - c

Question

I need to make a hash table program that will take the first character of a string in a small case letter and modulo the ASCII with the size of the hash table that the user input. Where should I input the size other than in the main?
These are my current codes. In this code, I ask the user to input the size in the main module function but I am confused about how to use it in on every function besides main. Any help is appreciated.
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<ctype.h>
struct data
{
char name [100];
char age[2];
struct data *next;
};
struct data *chain[size] = {NULL};
struct data* insert(char name[], char age[]){
struct data *curr = (struct data*) malloc (sizeof(data));
strcpy(curr->name, name);
printf("input name: ");
scanf(" %[^\n]s",strcpy(curr->name, name));
printf("input age: ");
scanf(" %[^\n]s", strcpy(curr->age, age));
curr->next = NULL;
return curr;
};
int main(){
int n;
char name[100];
char age[2];
char firstChar;
int key;
int index = 0;
printf("input the number of hash table: ");
scanf("%d", &n); getchar();
printf("\n");
int option;
do{
printf("=== Option Menu ===\n");
printf("1. insert data\n");
printf("2. delete data\n");
printf("3. search data\n");
printf("4. view data\n");
printf("5. exit\n");
printf("input option: ");
scanf("%d", &option); getchar();
switch(option){
case 1:
insert(name,age);
break;
}
}while(option!=5);
}

Answer 1

can i make the size of hashtable dynamic ?
Yes, you can, and you even need to, since you wrote "I need to make a hash table program … with the size of the hash table that the user input". In order to do that, don't define struct data *chain[size] = {NULL}; but struct data **chain; and after input of n in main do
chain = calloc(n, sizeof *chain);