Language: C

int main(void){
int a,b,c;
scanf("%d %d %d",&a,&b,&c);
if(a<b&&a<c)
 {
  a(a, b, c);
 }else if(b<c)
 {
  b(a, b, c);
 }else
 {
  c(a, b, c);
 }
return 0;
}

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

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

int c(int a, int b, 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:3:1: error: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
    3 | scanf("%d %d %d",&a,&b,&c);
      | ^~~~~
main.c:1:1: note: include '<stdio.h>' or provide a declaration of 'scanf'
  +++ |+#include <stdio.h>
    1 | int main(void){
main.c:3:1: warning: incompatible implicit declaration of built-in function 'scanf' [-Wbuiltin-declaration-mismatch]
    3 | scanf("%d %d %d",&a,&b,&c);
      | ^~~~~
main.c:3:1: note: include '<stdio.h>' or provide a declaration of 'scanf'
main.c:6:3: error: called object 'a' is not a function or function pointer
    6 |   a(a, b, c);
      |   ^
main.c:2:5: note: declared here
    2 | int a,b,c;
      |     ^
main.c:9:3: error: called object 'b' is not a function or function pointer
    9 |   b(a, b, c);
      |   ^
main.c:2:7: note: declared here
    2 | int a,b,c;
      |       ^
main.c:12:3: error: called object 'c' is not a function or function pointer
   12 |   c(a, b, c);
      |   ^
main.c:2:9: note: declared here
    2 | int a,b,c;
      |         ^
main.c: In function 'a':
main.c:20:3: error: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
   20 |   printf("%d %d %d\n",a,b,c);
      |   ^~~~~~
main.c:20:3: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:20:3: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
main.c:20:3: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:23:3: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   23 |   printf("%d %d %d\n",a,c,b);
      |   ^~~~~~
main.c:23:3: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c: In function 'b':
main.c:31:3: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   31 |   printf("%d %d %d\n",b,a,c);
      |   ^~~~~~
main.c:31:3: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:34:3: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   34 |   printf("%d %d %d\n",b,c,a);
      |   ^~~~~~
main.c:34:3: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c: In function 'c':
main.c:42:3: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   42 |   printf("%d %d %d\n",c,a,b);
      |   ^~~~~~
main.c:42:3: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:45:3: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   45 |   printf("%d %d %d\n",c,b,a);
      |   ^~~~~~
main.c:45:3: note: include '<stdio.h>' or provide a declaration of 'printf'