Creating a recursive function that creates a expression tree from a prefix expression (in a char array) in C

Each element (operands, operators, parenthese) in the prefix expression is seperated by a white space. These are some of the functions needed.

void createExpTree ( BTNode ** root , char * prefix );  void printTree ( BTNode * node );  void printTreePostfix ( BTNode * node );  

and this is the structure of the BTnode

typedef struct _btnode{  int item;  struct _btnode *left;  struct _btnode *right;  } BTNode;  

this is my code for the function createExpTree but I dont understand what is wrong

void createExpTree(BTNode** root,char* prefix)  {  int j, x;  char c;  char d[SIZE];    if (*prefix == '\0')      return;  if (*prefix == ' ')      prefix++;  c = *prefix;  if (c=='*' || c=='/' || c=='+' || c=='-') {      // if prefix exp is OPT      // create children      BTNode* nn = (BTNode*)malloc(sizeof(BTNode));      nn->item = c;      nn->left = NULL;      nn->right = NULL;      *root = nn;      prefix++;      createExpTree(&((*root)->left), prefix);      createExpTree(&((*root)->right), prefix);  }  else { //if prefix exp is OPERAND      j=0;      while (c!=' ') {          d[j]=c;          j++; prefix++;          c = *prefix;      }      d[j]='\0';      x = atoi(d);      BTNode* nn = (BTNode*)malloc(sizeof(BTNode));      nn->item = x;      nn->left = NULL;      nn->right = NULL;      *root = nn;      prefix++;      return;      }  }  

these are my codes for printTree and printTreePostfix

void printTree(BTNode *node){  if (node == NULL) {      return;  }  else {      printTree(node->left);      if(node->item >= 0 || node->item <= INT_MAX)          printf("%d ",node->item);      else          printf("%c ",(char)(node->item));      printTree(node->right);  }  }    void printTreePostfix(BTNode *node){  if (node == NULL) {      return;  }  else {      printTreePostfix(node->left);      printTreePostfix(node->right);      if(node->item >= 0 || node->item <= INT_MAX)          printf("%d ",node->item);      else          printf("%c ",(char)(node->item));  }  }  

The input for this question is something like "+ 99 / + 88 77 - * 66 - 55 44 33", the integers are presumably 2-digit integers. I can't seem to traverse the char array prefix recursively to get the individual pointers in order to create the expression tree.

Does prefix++ even traverse the char array correctly?? is the recursive function call createExpTree(&((*root)->right), prefix); missing anything??

Would appreciate any help!! Thanks!!

**Edited : noticed an error in creating newnode for operand

https://stackoverflow.com/questions/66828074/creating-a-recursive-function-that-creates-a-expression-tree-from-a-prefix-expre March 27, 2021 at 12:43PM