Thread: Pointer Error

Good day, I am having a pointer error in my string compare. can somebody please correct me? the program is reading have a rough text file of

abcde
ebcad
acdbe

and several same letters of the different orders and check which one is equal to the first one. I got the comparison right and it produces

ae
bb
cc
da
ed

and

aa
bc
cd
db
ee

so the output should be
bb
cc

and

aa
ee

but it's give me an error.

Code:

int main(void)
{

   FILE *fp;
   char *status, *status2;
   
   int times;
   int looptimes;
    
    struct
    {
	char numberofItems[2];
	char answersToQuestions[50];
    } answerKey[SIZEANS];
    
    struct
   {
	char studentID[7];
        char answers[50];
   } answer[SIZE];
 
   int y, szAns[] = {0,3,51};
   int i, sz[] = {0,6,51};
   char buff[1024];
   char buff2[1024];
   char insert[1024];
   int x = 0;   
   int w = 1;

   fp = fopen("Exam.txt","r");
   status = fgets(buff, sizeof(buff), fp);
   status2 = fgets(buff2,sizeof(buff2),fp);
   

   for(times = 0; times<1;times++)
   {
	strncpy(answerKey[times].numberofItems, strtok(buff," "), szAns[1]);
        strncpy(answerKey[times].answersToQuestions,strtok(NULL," "), szAns[2]);
	printf("%s %s",answerKey[times].numberofItems,answerKey[times].answersToQuestions);
        
	for(w = 0; w <= strlen(answerKey[times].answersToQuestions) - 2; w++)
	{
	   printf("%c\n",answerKey[times].answersToQuestions[w]);
	} 

   }

   while(status2 != NULL)
   {
	strncpy(answer[i].studentID, strtok(buff2," "),sz[1]);
	strncpy(answer[i].answers, strtok(NULL," "),sz[2]);
        printf("%s",answer[i].answers);
        
	for(x = 0; x<=strlen(answer[i].answers) - 1; x++)
	{	
		
		if(strcmp(answer[i].answers[x], answerKey[0].answersToQuestions[x]) == 0)
		{
		printf("%c",answer[i].answers[x]);
		printf("%c\n",answerKey[0].answersToQuestions[x]);
		}
		
	} 
	x = 0;
	i++;
	status2 = fgets(buff2,sizeof(buff2),fp);
   }  

printf("\n");
fclose(fp);
return 0;
}

to store string of 3 chars you need buffer of 4 chars
your buffer of 2 chars is only good for strings of 1 letter length

Code:

if(strcmp(answer[i].answers[x], answerKey[0].answersToQuestions[x]) == 0)
		{
		printf("%c",answer[i].answers[x]);
		printf("%c\n",answerKey[0].answersToQuestions[x]);
		}

strcmp is used to compare strings. if you want to compare single character just do it as you do with integer values:

Code:

if(answer[i].answers[x] == answerKey[0].answersToQuestions[x])
{
	printf("%c",answer[i].answers[x]);
	printf("%c\n",answerKey[0].answersToQuestions[x]);
}

Why do you need to print the same value twice?

Originally Posted by vart

Code:

if(strcmp(answer[i].answers[x], answerKey[0].answersToQuestions[x]) == 0)
		{
		printf("%c",answer[i].answers[x]);
		printf("%c\n",answerKey[0].answersToQuestions[x]);
		}

strcmp is used to compare strings. if you want to compare single character just do it as you do with integer values:

Code:

if(answer[i].answers[x] == answerKey[0].answersToQuestions[x])
{
	printf("%c",answer[i].answers[x]);
	printf("%c\n",answerKey[0].answersToQuestions[x]);
}

Why do you need to print the same value twice?

Code:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define SIZE 81
#define SIZEANS 81

int main(void)
{

   FILE *fp, *outFp;
   char *status, *status2;
   
   int times;
   int looptimes;
    
    struct
    {
	char numberofItems[3];
	char answersToQuestions[50];
    } answerKey[SIZEANS];
    
    struct
   {
	char studentID[7];
        char answers[50];
   } answer[SIZE];
 
   int y, szAns[] = {0,3,51};
   int i, sz[] = {0,6,51};
   char buff[1024];
   char buff2[1024];
   char insert[1024];
   int x = 0;   
   int w = 1;
   int s = 1;
   int temporary;
   const int percent = 100;
   int score = 0;
   int trialpo;

   fp = fopen("Examdat.txt","r");
   outFp = fopen("outputData.txt","w");
   status = fgets(buff, sizeof(buff), fp);
   status2 = fgets(buff2,sizeof(buff2),fp);
   

   for(times = 0; times<1;times++)
   {
	strncpy(answerKey[times].numberofItems, strtok(buff," "), szAns[1]);
        strncpy(answerKey[times].answersToQuestions,strtok(NULL," "), szAns[2]);
	printf("%s %s",answerKey[times].numberofItems,answerKey[times].answersToQuestions);

	fprintf(outFp,"\tExam Report\nQuestion");

	temporary = atoi(answerKey[times].numberofItems);
	for (s = 1; s <= temporary; s++)
	{
           fprintf(outFp,"\t%d",s);
	}
	
	fprintf(outFp,"\nAnswer");
	for(w = 0; w <= strlen(answerKey[times].answersToQuestions) - 2; w++)
	{
	   printf("%c\n",answerKey[times].answersToQuestions[w]);
	   fprintf(outFp,"\t     %c", answerKey[times].answersToQuestions[w]);
	}	    
   }
  
   fprintf(outFp,"\n\nID\t\tScore(%)\n");
   while(status2 != NULL)
   {
	strncpy(answer[i].studentID, strtok(buff2," "),sz[1]);
	strncpy(answer[i].answers, strtok(NULL," "),sz[2]); 

	
	fprintf(outFp,"%s", answer[i].studentID);
	printf("%d",strlen(answer[i].answers) - 1 );

	for(x = 0; x<=strlen(answer[i].answers) - 1; x++)
	{	
		if(answer[i].answers[x] == answerKey[0].answersToQuestions[x])
		{
		score += 1;
		printf("%c",answer[i].answers[x]);
		printf("%c\n",answerKey[0].answersToQuestions[x]);
		}	
	} 
	x = 0;
	
	status2 = fgets(buff2,sizeof(buff2),fp);

	
	//printf("%d\n",score - 2);
	//score /= temporary;
	//score *= percent;
	fprintf(outFp,"\t%d\n",score);
	i++;
	

	
   }  

printf("\n");
fclose(outFp);
fclose(fp);
return 0;
}

The problem is now that every time I put the string length of each of the text file, it's giving me a 665
instead of a 666,

so that means, my string length is decreasing?


is there a way to fix this? thanks.