Thread: curious runtime error!!

a few days ago, i helped my girlfriend to write a c program. the program collapseed when i inputed the data and press enter.
the source code:

Code:

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

#define STU_NAME_LEN 8
 
typedef struct
{
 char stuName[STU_NAME_LEN];
 float chinese;
 float math;
 float english;
} StudentInfo;
 
StudentInfo* stuArray = NULL;
int stuNum = 0;
 
int controlThread = 1;
int function = 0;
HANDLE Mutex;
void bubleSort(int i)
{
 int j;
 StudentInfo temp;
 float** select = malloc(sizeof(float*) * stuNum);
 if (select == NULL) exit(1);
 
 switch (i)
 {
 case 1: 
  {
   for (j=0; j<stuNum; j++) select[j] = &stuArray[j].chinese;
   break;
  } 
 case 2: 
  {
   for (j=0; j<stuNum; j++) select[j] = &stuArray[j].english;
   break;
  } 
 case 3: 
  {
   for (j=0; j<stuNum; j++) select[j] = &stuArray[j].math;
   break;
  }
 default: ;
 }
 for (i=stuNum; i>1; i--)
 {
  for (j=0; j<i - 1; j++)
  {
   if (*select[j] > *select[j + 1])
   {
    temp = stuArray[j];
    stuArray[j] = stuArray[j + 1];
    stuArray[j + 1] = temp;
   }
  }
 }
 
 free(select);
 return;
 
}
 
void sort()
{
 int i;
 printf("please input the subject that you want to set to the keyword\n\
1. chinese    2. english    3. math\n\
select: ");
 scanf("%d", &i);
 bubleSort(i);
 return;
}
 
void print()
{
 int i;
 printf("the detail information of the students : \n");
 for (i=0; i<stuNum; i++)
 {
  printf("%d. %s\n", i, stuArray[i].stuName);
  printf("english score : %g\n", stuArray[i].english);
  printf("chinese score : %g\n", stuArray[i].chinese);
  printf("math score : %g\n", stuArray[i].math);
  printf("\n");
 }
 return;
}
 
void search()
{
 int i;
 char name[STU_NAME_LEN];
 int j = 0;
 printf("input the name you search : ");
 scanf("%s", name);
 for (i=0; i<stuNum; i++)
 {
  if (strcmp(name, stuArray[i].stuName) == 0)
  {
   printf(" %s\n", stuArray[i].stuName);
   printf("english score : %g\n", stuArray[i].english);
   printf("chinese score : %g\n", stuArray[i].chinese);
   printf("math score : %g\n", stuArray[i].math);
   printf("\n");
  }
  j = 1;
 }
 if (j == 0) printf("no student\n");
 return;
}
 
void inputData()
{
 int i;
 for (i=0; i<stuNum; i++)
 {
  printf("input information of the %dth student:\n", i + 1);
  printf("student name: ");
  scanf("%s", stuArray[i].stuName);
  printf("chinese score: ");
  scanf("%f", &stuArray[i].chinese);   /*error*/
  printf("math score: ");
  scanf("%f", &stuArray[i].math);      /*error*/
  printf("english score: ");
  scanf("%f", &stuArray[i].english);    /*error*/
 }
 return;
}
 
void statistics()
{
 int i;
 double totalEnglishScore = 0.0,
     totalChineseScore = 0.0,
     totalMathScore = 0.0;
/* double max[3];  /*max[0] english , max[1] chinese , max[2] math
 double min[3];
 for (i=0; i<3; i++)
 {
  max[i] = 0.0;
  min[i] = 9999.9;
 }
*/
 for (i=0; i<stuNum; i++)
 {
  totalEnglishScore += stuArray[i].english;
  totalChineseScore += stuArray[i].chinese;
  totalMathScore += stuArray[i].math;
 }
 printf("the average score of english is : %g\n" , totalEnglishScore / stuNum);
 printf("the average score of chinese is : %g\n" , totalChineseScore / stuNum);
 printf("the average score of math is : %g\n" , totalMathScore / stuNum);
}
 
void welcome()
{
 printf("\
 *****************************************************\n\
 **************  homework of OS **********************\n\
 **************  author: 柯舒勤 **********************\n\
 ************** date: 2006.11.20 *********************\n\n");
 return;
}
 
unsigned __stdcall InputData(void* pArguments)
{
 while (controlThread)
 {
  if (function == 1)
  {
   WaitForSingleObject(Mutex, INFINITE);
   system("cls");
   welcome();
   inputData();
   function = 0;
   system("pause");
   ReleaseMutex(Mutex);
  }
  Sleep(200);
 }
 _endthreadex(0);
 return 0;
}
 
unsigned __stdcall Statistics(void* pArguments)
{
 while (controlThread)
 {
  if (function == 4)
  {
   WaitForSingleObject(Mutex, INFINITE);
   system("cls");
   welcome();
   statistics();
   function = 0;
   system("pause");
   ReleaseMutex(Mutex);
  }
  Sleep(200);
 }
 _endthreadex(0);
 return 0;
}
 
unsigned __stdcall Search(void* pArguments)
{
 while (controlThread)
 {
  if (function == 3)
  {
   WaitForSingleObject(Mutex, INFINITE);
   system("cls");
   welcome();
   search();
   function = 0;
   system("pause");
   ReleaseMutex(Mutex);
  }
  Sleep(200);
 }
 _endthreadex(0);
 return 0;
}
 
unsigned __stdcall Sort(void* pArguments)
{
 while (controlThread)
 {
  if (function == 2)
  {
   WaitForSingleObject(Mutex, INFINITE);
   system("cls");
   welcome();
   sort();
   print();
   function = 0;
   system("pause");
   ReleaseMutex(Mutex);
  }
  Sleep(200);
 }
 _endthreadex(0);
 return 0;
}
 
int main()
{ 
 int i;
    HANDLE hThread[4];
    unsigned threadID[4];
 
 Mutex = CreateMutex(NULL,FALSE,NULL);
 printf("Please input the number of the students : ");
 scanf("%d", &stuNum);
 stuArray = (StudentInfo*)malloc(sizeof(StudentInfo) * stuNum);
 if (stuArray == NULL) 
 {
  printf("allocate failed!");
  exit(1);
 }
    hThread[0] = (HANDLE)_beginthreadex(NULL, 0, &InputData, NULL, 0, &threadID[0]);
    hThread[1] = (HANDLE)_beginthreadex(NULL, 0, &Search, NULL, 0, &threadID[1]);
    hThread[2] = (HANDLE)_beginthreadex(NULL, 0, &Sort, NULL, 0, &threadID[2]);
    hThread[3] = (HANDLE)_beginthreadex(NULL, 0, &Statistics, NULL, 0, &threadID[3]);
 

 while (function != 5)
 {
  WaitForSingleObject(Mutex, INFINITE);
  system("cls");
  welcome();
  printf("1. input data  2. sort  3. search  4. statistic  5. exit   ");
  scanf("%d", &function);
 
  system("pause");
  if (function < 1 && function > 5) printf("error\n");
  ReleaseMutex(Mutex);
 }
 
 controlThread = 0;
 for (i=0; i<4; i++) WaitForSingleObject(hThread[i], INFINITE);
 for (i=0; i<4; i++) CloseHandle(hThread[i]);
 CloseHandle(Mutex);
 
 free(stuArray);
 return 0;
}

the error was caused by scanf("%f",&stuArray[i].chinese)
but i change the scanf("%f", .....) to scanf("%lf",.......), it run correctly. it is so curious that i can't understand,who can tell me why?my compile environment is vc.net(2003)

ps: sorry, i come from china, so i can't express my purpose correctly in english

Originally Posted by zouyu1983

i helped my girlfriend to write a c program

How romantic Anyways, %lf indicates a double, rather than a float.

Exactly, because you're scanning a double. Thus you use %lf.

Hmm, I don't know

If the variables are defined as float, then "%f" is the correct scanf usage.

However, that's not your only problem

new.c:32: warning: assignment from incompatible pointer type
new.c:37: warning: assignment from incompatible pointer type
new.c:42: warning: assignment from incompatible pointer type
For all these lines
for (j=0; j<stuNum; j++) select[j] = &stuArray[j].chinese;
They exist in the struct as floats, yet you compare and swap them as doubles.

This is going to corrupt the memory very severely.

> printf("please input the subject that you want to set to the keyword\n\
> 1. chinese 2. english 3. math\n\
> select: ");
The correct way to wrap long strings is like this

Code:

 printf("please input the subject that you want to set to the keyword\n"
        "1. chinese    2. english    3. math\n"
        "select: ");

Not all compilers will wrap long strings joined together with a \

Not all compilers will wrap long strings joined together with a \

Why not? The preprocessor handles that, and there's no reason it should replace \ at the end of lines elsewhere but not inside strings.

It's definitely true that not all compilers support newlines inside strings, though:

Code:

printf("Hello,
there");

Since this works

Code:

#define abs(x) \
    ((x) > 0 ? (x) : -(x))

I see no reason why this shouldn't

Code:

printf("Hello \
there");

Of course, I always do this anyway

Code:

printf("hello "
    "there");

so that I can indent the succeeding lines.

Am I missing something?

I see no reason why this shouldn't

Maybe because he first one is inside preprocessor's directive and the second one - not. Why preprocessor should bother to do something with the second slash?