how to encode my input string since I have build a Huffman tree and character corresponding code by C

this code now can be compiled, but only output the table of code and the minimum weighted external path length

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdbool.h>

#define MAX_TREE_HT 100

struct MinHeapNode {
    char data;
    unsigned freq;
    struct MinHeapNode *left, *right;
};

struct MinHeap {
    unsigned size;
    unsigned capacity;
    struct MinHeapNode** array;
};

struct MinHeapNode* newNode(char data, unsigned freq) {
    struct MinHeapNode* temp = (struct MinHeapNode*)malloc(sizeof(struct MinHeapNode));
    temp->left = temp->right = NULL;
    temp->data = data;
    temp->freq = freq;

    return temp;
}

struct MinHeap* createMinHeap(unsigned capacity) {
    struct MinHeap* minHeap = (struct MinHeap*)malloc(sizeof(struct MinHeap));
    minHeap->size = 0;
    minHeap->capacity = capacity;
    minHeap->array = (struct MinHeapNode**)malloc(minHeap->capacity * sizeof(struct MinHeapNode*));

    return minHeap;
}

void swapMinHeapNode(struct MinHeapNode** a,
                     struct MinHeapNode** b) {
    struct MinHeapNode* t = *a;
    *a = *b;
    *b = t;
}

void minHeapify(struct MinHeap* minHeap, int idx) {
    int smallest = idx;
    int left = 2 * idx + 1;
    int right = 2 * idx + 2;

    if (left < minHeap->size && 
        minHeap->array[left]->freq < minHeap->array[smallest]->freq)
        smallest = left;

    if (right < minHeap->size && 
        minHeap->array[right]->freq < minHeap->array[smallest]->freq)
        smallest = right;

    if (smallest != idx) {
        swapMinHeapNode(&minHeap->array[smallest],
                        &minHeap->array[idx]);
        minHeapify(minHeap, smallest);
    }
}

int isSizeOne(struct MinHeap* minHeap) {
    return (minHeap->size == 1);
}

struct MinHeapNode* extractMin(struct MinHeap* minHeap) {
    struct MinHeapNode* temp = minHeap->array[0];
    minHeap->array[0] = minHeap->array[minHeap->size - 1];

    --minHeap->size;
    minHeapify(minHeap, 0);

    return temp;
}

void insertMinHeap(struct MinHeap* minHeap,
                   struct MinHeapNode* minHeapNode) {
    ++minHeap->size;
    int i = minHeap->size - 1;

    while (i && minHeapNode->freq < minHeap->array[(i - 1) / 2]->freq) {
        minHeap->array[i] = minHeap->array[(i - 1) / 2];
        i = (i - 1) / 2;
    }

    minHeap->array[i] = minHeapNode;
}

void buildMinHeap(struct MinHeap* minHeap) {
    int n = minHeap->size - 1;
    int i;

    for (i = (n - 1) / 2; i >= 0; --i)
        minHeapify(minHeap, i);
}

void printArr(int arr[], int n) {
    int i;
    for (i = 0; i < n; i++) {
        printf("%d",arr[i]);
    }

    printf("\n");
}

here I want to make a function to encode the input string ,can anyone help?

void encode(struct MinHeapNode* root, int arr[], int n) {

}

int isLeaf(struct MinHeapNode* root) {
    return !(root->left) && !(root->right);
}

struct MinHeap* createAndBuildMinHeap(char data[], int freq[], int size) {
    struct MinHeap* minHeap = createMinHeap(size);

    for (int i = 0; i < size; ++i)
        minHeap->array[i] = newNode(data[i], freq[i]);

    minHeap->size = size;
    buildMinHeap(minHeap);

    return minHeap;
}

struct MinHeapNode* buildHuffmanTree(char data[],int freq[], int size) {
    struct MinHeapNode *left, *right, *top;

    struct MinHeap* minHeap = createAndBuildMinHeap(data, freq, size);

    while (!isSizeOne(minHeap)) {
        left = extractMin(minHeap);
        right = extractMin(minHeap);
        top = newNode('$', left->freq + right->freq);

        top->left = left;
        top->right = right;

        insertMinHeap(minHeap, top);
    }

    return extractMin(minHeap);
}

void printCodes(struct MinHeapNode* root, int arr[], int top) {
    if (root->left) {
        arr[top] = 0;
        printCodes(root->left, arr, top + 1);
    }

    if (root->right) {
        arr[top] = 1;
        printCodes(root->right, arr, top + 1);
    }

    if (isLeaf(root)) {
        printf("%c:", root->data);
        printArr(arr, top);
    }
}

void HuffmanCodes(char data[], int freq[], int size) {
    struct MinHeapNode* root = buildHuffmanTree(data, freq, size);

    int arr[MAX_TREE_HT], top = 0;

    printCodes(root,arr,top);
}

int main() {
    char input;
    int i = 0;
    char plaintext[20];
    int counta = 0, countb = 0, countc = 0;

    while (scanf("%c", &input) != EOF) {
        if (input == 'a') {
            plaintext[i] = 'a';
            counta++;
        }

        if (input == 'b') {
            plaintext[i] = 'b';
            countb++; 
        }

        if (input == 'c') {
            plaintext[i] = 'c';
            countc++; 
        }

        i++;
    }

    char arr[] = {'a', 'b', 'c'};
    int freq[] = {counta, countb, countc};

    int size = sizeof(arr) / sizeof(arr[0]);
    HuffmanCodes(arr, freq, size);

    int counting[3];
    counting[0] = counta;
    counting[1] = countb;
    counting[2] = countc;

    if (counting[0] < counting[1]) {
        int temp = counting[0];
        counting[0] = counting[1];
        counting[1] = temp;
    }

    if (counting[2] > counting[0]) {
        counting[0] = counting[2];
    }

    int sum = counting[0] * 1 + counting[1] * 2 + counting[2] * 2;
    printf("> %d", sum);

    return 0;
}

I supposed to read the character code into an array but I don't know how to send input string into any function and get encoding

problem discription