在 C 中添加和打印数组元素

Question

This is a function that is trying to perform the first step of converting a CFG to Chromsky Normal From by adding 0->S as a rule to the end of the list of rules. My rules are an array of characters. For some reason it will only print the array the first time and not any time after that. I want it to print the input and then result once the array has been edited. I cannot figure out why it won't print. The output is just the original input and then blank spaces.

UPDATE: It will now print both times, but the output of the second print is the same as the first. It is not registering that I added ',','0','>','S' as elements to the array. Am I adding the elements wrong?

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

//global variables
char stringCFG[200];

//a program to convert CFG to Chromsky Normal Form
int main(int argc, char *argv[]){
  //intialize instance variables
  FILE *CFG;
  FILE *output;
  char ch;
  int RHS= 0;
  int isThereS= 0;
  int howManyItems= 0;

  CFG= fopen(argv[1], "r");
  output= fopen(argv[2], "w");
  
  for (int i=0; i<200; i++){
      fscanf(CFG, "%c", &stringCFG[i]);
      howManyItems++;
      fprintf(output,"%c", stringCFG[i]);
  }
  printf("\n");

  for(int i=0; i<200; i++){
    if(stringCFG[i] == '>'){
      RHS= 1;
    }
    if(stringCFG[i] == ','){
      RHS= 0;
    }
    if(RHS== 1){
      if(stringCFG[i] == 'S'){
        isThereS=1;
      }
    }
  }

  if(isThereS==1){
    stringCFG[howManyItems]= ',';
    howManyItems++;
    stringCFG[howManyItems]='0';
    howManyItems++;
    stringCFG[howManyItems]='>';
    howManyItems++;
    stringCFG[howManyItems]='S';
    howManyItems++;
  }
 for(int i=0; i<200; i++){
   fprintf(output,"%c",stringCFG[i]);
  }
  fclose(CFG);
  fclose(output);
}

Answer 1

The problem seems to be here:

  for (int i=0; i<200; i++){
      fscanf(CFG, "%c", &stringCFG[i]);
      howManyItems++;
      fprintf(output,"%c", stringCFG[i]);
  }

This loop always executes 200 times regardless of what is in the file. In other words - the value of howManyItems will be 200 when the loop is done.

You can check that simply by printing howManyItems after the loop, ie

printf("After loop, howManyItems=%d\n", howManyItems);

Since you have:

char stringCFG[200];

then

stringCFG[howManyItems]= ',';  // bad.. writing to stringCFG[200]
howManyItems++;
stringCFG[howManyItems]= '0';  // bad.. writing to stringCFG[201]
howManyItems++;
...

will write outside of the array. That is undefined behavior.

You need to stop the first loop once the whole file has been read. Something like:

  for (int i=0; i<200; i++){
      if (fscanf(CFG, "%c", &stringCFG[i]) != 1)
      {
          // No more data
          break;
      }
      howManyItems++;
      fprintf(output,"%c", stringCFG[i]);
  }

and all the following loops must then use howManyItems as the upper limit.

Like

  for(int i=0; i<howManyItems; i++){
    if(stringCFG[i] == '>'){
      RHS= 1;
    }
    ...
  }

BTW: Since you want to be able to add 4 extra chars, you probably should do:

char stringCFG[200]; --> char stringCFG[200 + 4];

BTW: Hard-coding the value 200 over and over again is bad practice. Instead use a define like:

#define MAX_CHARS 200

and replace all the hard-coded 200 with MAX_CHARS . Then you can adjust the maximum simply by editing one line instead of multiple lines.