Thread: Storing information in Arrays: Crash in Windows or Error in Linux

I have an error happening here.
1. I have attempted to write this function while I am learning C. It asks how many students and then asks for the age of each student.

2. In Windows after 4 ages I get a crash that says its not working and it feezes. In linux I receive this error:

studentAge.c: In function 'main':
studentAge.c:30:5: error: format '%d' expects argument of type 'int *', but argument 2 has type 'int' [-Werror=format]

Code:

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

int main(int argc, char *argv[])
{
  int numOfStudents=0,studentsAge[numOfStudents],a;  
      for(a=2;a>0;a--) {
      printf("How many students do you have (1-10)? ");
      if (scanf("%d*c",&numOfStudents)) {
        if(numOfStudents<0) {
        printf("Come on, how can you have a class with %d number of students?\n",numOfStudents);
        a=2;
        }
        else if(numOfStudents>10) {
        printf("Your class cannot hold more than 10 students.\n");
        a=2;
        }
        else
         a=0;
      }
      else {
        printf("A valid number was not entered.  This program will now exit.\n");
        numOfStudents=0;
        a=0;
      }
    }
  printf("What are your students ages?\n");
  for(a=0;a<numOfStudents;a++) {
    printf("%d: ",a+1);
    scanf("%d",studentsAge[a]);
  }
  system("PAUSE");	
  return 0;
}

Can someone please point me in the correct direction as to why this is happening?

Thanks,

I understand that numOfStudents could be a char over an int.
If I knew what the error meant I would listen to it however I have never seen that error before. Line 30 is the scanf("....

Just figured it out. The scanf doesn't have an & in front of the array.

I am just learning so I would much appreciate if you wanted to compile and tell me what other mistakes I should not be making. This would help me become a better programmer. I just found out that system("PAUSE"); apparently doesn't work in Linux. It compiles just fine however when you run the program it errors out stating that it could not find that command so that must be a Windows thing.

Here is the revised code. This was merely for a project that I was working on for some video tutorials. The tutorials are stupidly easy so I am attempting to make them a little harder by added my own twist to the required coding. If you want to compile it and look at it that would be great. I know that conio.h is a Windows thing. Other than that what seems to be the issue. This program merely figures out the average age for the students in a class of up to 10.

Code:

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

int main(int argc, char *argv[])
{
  char numOfStudents=0,studentsAge[numOfStudents],a=0,b=0;
  float sum=0;
      for(a=2;a>0;a--) {
      printf("How many students do you have (1-10)? ");
      if (scanf("%d*c",&numOfStudents)) {
        if(numOfStudents<0) {
        printf("Come on, how can you have a class with %d number of students?\n",numOfStudents);
        a=2;
        }
        else if(numOfStudents>10) {
        printf("Your class cannot hold more than 10 students.\n");
        a=2;
        }
        else
         a=0;
      }
      else {
        printf("A valid number was not entered.  This program will now exit.\n");
        numOfStudents=0;
        a=0;
      }
    }
  printf("What are your students ages? (5-65)\n");
  for(b=0;b<numOfStudents;b++) {
    printf("Student %d: ",b+1);
    if (scanf("%d*c",&studentsAge[b])) {
        if(studentsAge[b]<5) {
        printf("The youngest student allowed in this class is 5.\n",numOfStudents);
        b=b-1;
        }
        else if(studentsAge[b]>65) {
        printf("The oldest person allowed in this class is 65\n");
        b=b-1;
        }
        else {
        sum=sum+studentsAge[b];
        }
      }
      else {
        printf("A valid number was not entered.  This program will now exit.\n");
        sum=0;
        numOfStudents=0;
        b=0;
      }
  }
  if(sum>0) {
  printf("The total added age of every student is: %.00f\n",sum);
  printf("The average age of the students is %.02f.\n",sum/(float)numOfStudents);
  }
  system("PAUSE");	
  return 0;
}

Thank you very much for that insight.
I read the Bridge Out Ahead in your signature and laughed... lol
I have taken both of your suggestions in to account and added more on to the program.

Thank you for the System("PAUSE") functionality. I should have recognized that because I do write Batch. I didn't make the connection however.

Laserlight, thank you for letting me know about the array initialization. I have fixed that.

I have added a few more lines of code and commented everything. Thanks for all of your assistance.

In linux, I have gedit set to treat all warnings as errors. In Dev-C++ I don't know how to set that up yet. I have used Visual Studio before but it has A LOT more than what I need at this point and I don't know everything that it does. I will probably switch over to that when I have a better understanding of errors and can understand debugging a little better.

Here is the newest copy of the code. It compiles and works perfectly

Code:

/*********************************************/
/* This program will ask how many students   */
/* are in the class.  Based upon your answer */
/* it will then ask what the ages are for    */
/* each student.  From the answers provided  */
/* it will round to the nearest whole number */
/* the average age for the class.            */
/*********************************************/
#include <stdio.h> // Allows printf() function
#include <math.h> // Allows the roundf function to be used.

int main(int argc, char *argv[])
{
// introduce and initialize the variables to be used within the program.
  char numOfStudents=0,a=0,b=0;
  float sum=0,average=0;

// Since we need to repeat the question if a wrong answer is provided we use a for loop.
// The if statements determine whether or not a correct answer was provided.
      for(a=2;a>0;a--) {
      printf("How many students do you have (1-10)? ");
      if (scanf("%d*c",&numOfStudents)) {
        if(numOfStudents<1) {
          printf("Come on, how can you have a class with %d students?\n",numOfStudents);
          a=2;
        }
        else if(numOfStudents>10) {
          printf("Your class cannot hold more than 10 students.\n");
          a=2;
        }
        else
          a=0;
      }
      else {
        printf("A valid number was not entered.  This program will now exit.\n");
        numOfStudents=0;
        a=0;
      }
    }
// Now that we know how many Students we have in the class, we need to initialize the array.
    char studentsAge[numOfStudents];

// First, test to see if we made it out of the for loop above with a correct answer.
// Then ask a proper question with the switch statement based upon the number of students
   if(numOfStudents>0) {
    switch(numOfStudents) {
      case 1: printf("What is your students age? (5-65)\n");
      break;
      default: printf("What are your students ages? (5-65)\n");
    }
   }

// Great, we have made it asking about the age of the students.  Here we are going to use a
// for loop to determine what the students ages are just like we did above.
// We exit the program if a valid number is not entered.
  for(b=0;b<numOfStudents;b++) {
    printf("Student %d: ",b+1);
    if (scanf("%d*c",&studentsAge[b])) {
        if(studentsAge[b]<5) {
          printf("The youngest student allowed in this class is 5.\n",numOfStudents);
          b=b-1;
        }
        else if(studentsAge[b]>65) {
          printf("The oldest person allowed in this class is 65\n");
          b=b-1;
        }
        else {
          sum=sum+studentsAge[b]; // Used to add up all of the students ages
        }
      }
      else {
        printf("A valid number was not entered.  This program will now exit.\n");
        sum=0;
        numOfStudents=0;
        b=0;
      }
  }

// Check to see if sum is greater than 0.  If it is then we must have a correct answer for both numOfStudents and sum.
// We display the combined ages for everyone in the class.  We now figure out the average age for the class and display it.
  if(sum>0) {
    average=sum/(float)numOfStudents;
    printf("The total added age of every student is: %.00f\n",sum);
    printf("The average age of the students is %.0f.\n",roundf(average));
  }
  system("PAUSE"); // Proprietary to Windows. Keeps the command line window open when it reaches the end of the program.
  return 0;
}