Language: C

int main(n,i){int f[9] = {};double a;for(scanf("%d",&n),i=n;scanf("%lf",a),i;--i)a<165?f[1]++:a<170?f[2]++:a<175?f[3]++:a<180?f[4]++:a<185?f[5]++:f[6]++;for(i=1;i<7;puts(""),++i)for(printf("%d:",i),n=0;j<f[i];++n)printf("*");}

Compiler output:
main.c: In function 'main':
main.c:1:5: error: type of 'n' defaults to 'int' [-Wimplicit-int]
    1 | int main(n,i){int f[9] = {};double a;for(scanf("%d",&n),i=n;scanf("%lf",a),i;--i)a<165?f[1]++:a<170?f[2]++:a<175?f[3]++:a<180?f[4]++:a<185?f[5]++:f[6]++;for(i=1;i<7;puts(""),++i)for(printf("%d:",i),n=0;j<f[i];++n)printf("*");}
      |     ^~~~
main.c:1:5: error: type of 'i' defaults to 'int' [-Wimplicit-int]
main.c:1:42: error: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
    1 | int main(n,i){int f[9] = {};double a;for(scanf("%d",&n),i=n;scanf("%lf",a),i;--i)a<165?f[1]++:a<170?f[2]++:a<175?f[3]++:a<180?f[4]++:a<185?f[5]++:f[6]++;for(i=1;i<7;puts(""),++i)for(printf("%d:",i),n=0;j<f[i];++n)printf("*");}
      |                                          ^~~~~
main.c:1:1: note: include '<stdio.h>' or provide a declaration of 'scanf'
  +++ |+#include <stdio.h>
    1 | int main(n,i){int f[9] = {};double a;for(scanf("%d",&n),i=n;scanf("%lf",a),i;--i)a<165?f[1]++:a<170?f[2]++:a<175?f[3]++:a<180?f[4]++:a<185?f[5]++:f[6]++;for(i=1;i<7;puts(""),++i)for(printf("%d:",i),n=0;j<f[i];++n)printf("*");}
main.c:1:42: warning: incompatible implicit declaration of built-in function 'scanf' [-Wbuiltin-declaration-mismatch]
    1 | int main(n,i){int f[9] = {};double a;for(scanf("%d",&n),i=n;scanf("%lf",a),i;--i)a<165?f[1]++:a<170?f[2]++:a<175?f[3]++:a<180?f[4]++:a<185?f[5]++:f[6]++;for(i=1;i<7;puts(""),++i)for(printf("%d:",i),n=0;j<f[i];++n)printf("*");}
      |                                          ^~~~~
main.c:1:42: note: include '<stdio.h>' or provide a declaration of 'scanf'
main.c:1:166: error: implicit declaration of function 'puts' [-Wimplicit-function-declaration]
    1 | int main(n,i){int f[9] = {};double a;for(scanf("%d",&n),i=n;scanf("%lf",a),i;--i)a<165?f[1]++:a<170?f[2]++:a<175?f[3]++:a<180?f[4]++:a<185?f[5]++:f[6]++;for(i=1;i<7;puts(""),++i)for(printf("%d:",i),n=0;j<f[i];++n)printf("*");}
      |                                                                                                                                                                      ^~~~
main.c:1:166: note: include '<stdio.h>' or provide a declaration of 'puts'
main.c:1:183: error: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
    1 | int main(n,i){int f[9] = {};double a;for(scanf("%d",&n),i=n;scanf("%lf",a),i;--i)a<165?f[1]++:a<170?f[2]++:a<175?f[3]++:a<180?f[4]++:a<185?f[5]++:f[6]++;for(i=1;i<7;puts(""),++i)for(printf("%d:",i),n=0;j<f[i];++n)printf("*");}
      |                                                                                                                                                                                       ^~~~~~
main.c:1:183: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:1:183: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
main.c:1:183: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:1:203: error: 'j' undeclared (first use in this function)
    1 | int main(n,i){int f[9] = {};double a;for(scanf("%d",&n),i=n;scanf("%lf",a),i;--i)a<165?f[1]++:a<170?f[2]++:a<175?f[3]++:a<180?f[4]++:a<185?f[5]++:f[6]++;for(i=1;i<7;puts(""),++i)for(printf("%d:",i),n=0;j<f[i];++n)printf("*");}
      |                                                                                                                                                                                                           ^
main.c:1:203: note: each undeclared identifier is reported only once for each function it appears in