Best way to declare specific width variables depending on user input - c

Question

I have a code which looks as shown below. The code here is if the word_size = 64. In similar fashion I need to have for 32 and 16 too. I can't find a way to reuse the same encrypt function for all the sizes. Moreover, I need to declare the variables too according to the word_size, ie. to use either uint_16 or uint_32 or uint_64 depends upon word_size. Can you help me with writing a reusable code in this case?
#include<stdio.h>
#include<stdint.h>
void encrypt(uint64_t* , uint64_t*, uint64_t*);
int main(){
int block_size;
// Get the user inputs
printf("input the block size: \n");
scanf("%d", &block_size); // can be 32, 64 or 128
int word_size = block_size/2; // 16,32 or 64
// Depending on the word_size, I should declare the variables with
// corresponding width
uint64_t plain_text[2] = {0,0};
uint64_t cipher_text[2] = {0,0};
uint64_t key_text[2] = {0,0};
uint64_t * pt, *ct, *k;
encrypt(pt, ct,k);
}
/*
* Ecnryption Method
*/
void encrypt(uint64_t* pt, uint64_t* ct, uint64_t* k){
// Involves bit shifting algorithm which works only on exact sizes i.e eiter 16,32 or 64.
}
I can provide more information if needed.

Answer 1

There is a way to do this in C - by using struct and union
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <inttypes.h>
enum type {
U64,
U32,
U16,
U8,
};
struct container {
enum type type;
union {
uint64_t u64;
uint32_t u32;
uint16_t u16;
uint8_t u8;
} value;
};
int test(struct container container) {
switch(container.type) {
case U64:
printf("Value is :%" PRIu64 "\n", container.value);
break;
case U32:
printf("Value is :%" PRIu32 "\n", container.value);
break;
case U16:
printf("Value is :%" PRIu16 "\n", container.value);
break;
case U8:
printf("Value is :%" PRIu8 "\n", container.value);
break;
}
return 0;
}
int main(int argc, char **argv) {
struct container c1, c2;
c1.type = U64;
c1.value.u64 = 10000000000ULL;
c2.type = U8;
c2.value.u8 = 100;
test(c1);
test(c2);
return 0;
}
The output produced was:
Value is :10000000000
Value is :100