Language: C

int main()
{
 int a,b,c;
 if(a<b)
 {
  if(b<c||a<c)
  {
   a();
  }
 }else if(b<c)
 {
  b();
 }else
 {
  c();
 }
 return 0;
}

int a()
{
 if(b<c)
 {
  printf("%d %d %d\n",a,b,c);
 }else
 {
  printf("%d %d %d\n",a,c,b);
 }
 return 0;
}

int b()
{
 if(a<c)
 {
  printf("%d %d %d\n",b,a,c);
 }else
 {
  printf("%d %d %d\n",b,c,a);
 }
 return 0;
}

int c()
{
 if(a<b)
 {
  printf("%d %d %d\n",c,a,b);
 }else
 {
  printf("%d %d %d\n",c,b,a);
 }
 return 0;
}

Compiler output:
main.c: In function 'main':
main.c:8:4: error: called object 'a' is not a function or function pointer
    8 |    a();
      |    ^
main.c:3:6: note: declared here
    3 |  int a,b,c;
      |      ^
main.c:12:3: error: called object 'b' is not a function or function pointer
   12 |   b();
      |   ^
main.c:3:8: note: declared here
    3 |  int a,b,c;
      |        ^
main.c:15:3: error: called object 'c' is not a function or function pointer
   15 |   c();
      |   ^
main.c:3:10: note: declared here
    3 |  int a,b,c;
      |          ^
main.c: In function 'a':
main.c:22:5: error: 'b' undeclared (first use in this function)
   22 |  if(b<c)
      |     ^
main.c:22:5: note: each undeclared identifier is reported only once for each function it appears in
main.c:22:7: error: 'c' undeclared (first use in this function)
   22 |  if(b<c)
      |       ^
main.c:24:3: error: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
   24 |   printf("%d %d %d\n",a,b,c);
      |   ^~~~~~
main.c:1:1: note: include '<stdio.h>' or provide a declaration of 'printf'
  +++ |+#include <stdio.h>
    1 | int main()
main.c:24:3: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   24 |   printf("%d %d %d\n",a,b,c);
      |   ^~~~~~
main.c:24:3: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:27:3: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   27 |   printf("%d %d %d\n",a,c,b);
      |   ^~~~~~
main.c:27:3: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c: In function 'b':
main.c:34:7: error: 'c' undeclared (first use in this function)
   34 |  if(a<c)
      |       ^
main.c:36:3: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   36 |   printf("%d %d %d\n",b,a,c);
      |   ^~~~~~
main.c:36:3: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:39:3: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   39 |   printf("%d %d %d\n",b,c,a);
      |   ^~~~~~
main.c:39:3: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c: In function 'c':
main.c:48:3: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   48 |   printf("%d %d %d\n",c,a,b);
      |   ^~~~~~
main.c:48:3: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:51:3: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   51 |   printf("%d %d %d\n",c,b,a);
      |   ^~~~~~
main.c:51:3: note: include '<stdio.h>' or provide a declaration of 'printf'