View Compilation Error

0_0_22132297_31269.c: In function 'main':
0_0_22132297_31269.c:1:8: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
 main(){for(double a,b,c,m,n,l;~scanf("%lf%lf%lf%lf%lf%lf",&a,&c,&b,&n,&l,&m);b*=b,c*=c,m=b+c-m*m,n=c+a-n*n,l=a+b-l*l,printf("%.4f\n",sqrt(4*a*b*c-a*m*m-b*n*n-c*l*l+m*n*l)/12))a*=a;}
        ^
0_0_22132297_31269.c:1:8: note: use option -std=c99, -std=gnu99, -std=c11 or -std=gnu11 to compile your code