GCC kompilieren Fehler conflicting types

Ich eine Fehlermeldung vom GCC, wenn Sie versuchen, um diesen code zu kompilieren.

test.c: At top level:
test.c:35: error: conflicting types for âprintCoursesâ
test.c:4: error: previous declaration of âprintCoursesâ was here
test.c:59: error: conflicting types for âidSortâ
test.c:5: error: previous declaration of âidSortâ was here
test.c:100: error: conflicting types for âcourseSortâ
test.c:6: error: previous declaration of âcourseSortâ was here
test.c:137:2: warning: no newline at end of file

Ist, dass der Fehler bin ich immer, wenn jemand könnte bitte helfen. Ich bin versuchen zu organisieren, ein Struktur-array (OHNE Verwendung von qsort) und dann Sortieren Sie es erneut mit einem anderen parameter. Hier ist mein code:

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

void printCourses(struct courses *classList, int left, int size);
void idSort(struct courses *classList, int left, int right);
void courseSort(struct courses *classList, int left, int right);

//STRUCTURE 

struct courses
{
char course[50];
char courseName[50];
int courseID;
};

//MAIN

int main(void)
{
    int a, b,temp,i;
    int size = 11;
    struct courses classList[11]={{"MATH", "Linear Algebra", 3330},{"CSE", "Discrete         
    Structures", 2315},{"CSE","Intermediate Programming",1320},{"IE","Engineering Economics",  3312},{"CSE","Computer Organization", 2312},
    {"MATH","Calculus I",1426},{"CSE","Introductory Programming", 1310},{"MATH","Calculus II", 2425},{"IE","Engineering Statistics",3301},{"CSE","Operating Systems", 3320},{"CSE","Data Structures and Algorithms", 2320}};

    courseSort(classList, 0, size-1);
    printCourses(classList, 0, size-5);
}

//FUNCTION 1

void printCourses(struct courses *classList, int left, int size)
{
     int l,r;
     if( left < size)
     {
         l = left;

         printf("%s\n",classList[left].course);
         printf("------------------------------------\n");
         while( l < size )
         {
             printf("%d %s\n",classList[l].courseID,classList[l].courseName);
             l++;
         }

         printCourses(classList,left+6,size+2);
         printCourses(classList,left+8,size+5);
    }

}


//FUNCTION 2

void idSort(struct courses *classList, int left, int right)
{

  int pivot, l, r, comp, comp1;
  struct courses temp;
  if(left < right) 
  {
    pivot = left; 
    l = left;
    r = right;
    while(l < r) 
{

    while(classList[l].courseID <= classList[pivot].courseID && l <= right)

            l++;

    while(classList[r].courseID > classList[pivot].courseID && r >= left)

            r--;

  if(l < r ) 
  {
      temp = classList[l];
      classList[l] = classList[r];
      classList[r] = temp;
  }
}


temp = classList[r];
classList[r] = classList[pivot];
classList[pivot] = temp;

idSort(classList, left, r-1);
idSort(classList, r+1, right);
  }
}

//FUNCTION 3

void courseSort(struct courses *classList, int left, int right)
{
  int pivot, l, r, comp, comp1;
  struct courses temp;
  if(left < right) 
  {
    pivot = left; 
    l = left;
    r = right;

    while(l < r) 
    {

    while(strcmp(classList[l].course, classList[pivot].course) <= 0 && l <= right)
            l++;
    while(strcmp(classList[r].course, classList[pivot].course) > 0 && r > left)
            r--;

  if (l < r)
  {
      temp = classList[l];
      classList[l] = classList[r];
      classList[r] = temp;
  }
}


temp = classList[r];
classList[r] = classList[pivot];
classList[pivot] = temp;

courseSort(classList, left, r-1);
courseSort(classList, r+1, right);

}
idSort(classList,left,right-5);
idSort(classList,left+6,right-3);
idSort(classList,left+8,right-1);
}