simple bst in c

#include <stdio.h>
#include <stdlib.h>

struct node {
    struct node *levo;
    struct node *pravo;
    struct node *verx;
    int value;
    int key;
};

struct node *searchnode(struct node *derevo, int key);

struct node *findmin(struct node *derevo) {
    while (derevo->levo) {
        derevo = derevo->levo;
    }
    return derevo;
}

struct node *delnode(struct node *derevo, int key) {
    struct node *deleting = searchnode(derevo, key);
    if (!deleting) {
        return derevo;
    }

    if (deleting->pravo == NULL && deleting->levo == NULL) {
        if (deleting->verx) {
            if (deleting->verx->levo == deleting) {
                deleting->verx->levo = NULL;
            } else {
                deleting->verx->pravo = NULL;
            }
            free(deleting);
            return derevo;
        } else {
            free(deleting);
            return NULL;
        }
    }

    if (deleting->pravo && deleting->levo) {
        struct node *nextnode = findmin(deleting->pravo);
        deleting->key = nextnode->key;
        deleting->value = nextnode->value;
        if (nextnode->pravo) {
            if (nextnode->verx == deleting) {
                deleting->pravo = nextnode->pravo;
                nextnode->pravo->verx = deleting;
            } else {
                nextnode->verx->levo = nextnode->pravo;
                nextnode->pravo->verx = nextnode->verx;
            }
        } else {
            if (nextnode->verx == deleting) {
                deleting->pravo = NULL;
            } else {
                nextnode->verx->levo = NULL;
            }
        }
        free(nextnode);
        return derevo;
    }

    if (deleting->pravo) {
        if (deleting->verx) {
            if (deleting->verx->pravo == deleting) {
                deleting->verx->pravo = deleting->pravo;
            } else {
                deleting->verx->levo = deleting->pravo;
            }
            deleting->pravo->verx = deleting->verx;
        } else {
            derevo = derevo->pravo;
            derevo->verx = NULL;
        }
        free(deleting);
        return derevo;
    }

    if (deleting->verx) {
        if (deleting->verx->pravo == deleting) {
            deleting->verx->pravo = deleting->levo;
        } else {
            deleting->verx->levo = deleting->levo;
        }
        deleting->levo->verx = deleting->verx;
    } else {
        derevo = derevo->levo;
        derevo->verx = NULL;
    }
    free(deleting);
    return derevo;
}

struct node *addnode(struct node *derevo, int key, int value) {
    struct node *node = derevo;
    struct node *prev = NULL;
    while (node) {
        if (key > node->key) {
            prev = node;
            node = node->pravo;
        } else if (key < node->key) {
            prev = node;
            node = node->levo;
        } else {
            node->value = value;
            return derevo;
        }
    }
    node = malloc(sizeof(struct node));
    node->key = key;
    node->value = value;
    node->verx = prev;
    node->levo = NULL;
    node->pravo = NULL;
    if (!prev) {
        return node;
    }
    if (key > prev->key) {
        prev->pravo = node;
    } else {
        prev->levo = node;
    }
    return derevo;
}

struct node *searchnode(struct node *derevo, int key) {
    while (derevo) {
        if (key > derevo->key) {
            derevo = derevo->pravo;
        } else if (key < derevo->key) {
            derevo = derevo->levo;
        } else {
            return derevo;
        }
    }
    return NULL;
}

void cleanderevo(struct node *derevo) {
    if(derevo == NULL){
        return;
    }
    if(derevo->levo){
        cleanderevo(derevo->levo);
    }
    if(derevo->pravo){
        cleanderevo(derevo->pravo);
    }
    free(derevo);
}

int main(void) {
    struct node *derevo = NULL;
    char c;
    int k, v;
    scanf("%c", &c);
    while (c != 'F') {
        if (c == 'A') {
            scanf("%d %d", &k, &v);
            derevo = addnode(derevo, k, v);
        } else if (c == 'D') {
            scanf("%d", &k);
            derevo = delnode(derevo, k);
        } else if (c == 'S') {
            scanf("%d", &k);
            struct node *poisk = searchnode(derevo, k);
            if (poisk) {
                printf("%d %d\n", poisk->key, poisk->value);
            }
        }
        scanf("%c", &c);
    } // A = 65, D = 68, S = 83, F = 70
    cleanderevo(derevo);
}