View Compilation Error

0_0_14260997_17157.c:6:11: error: variably modified 'f' at file scope
 int T,n,m,f[maxn],a[10];
           ^
0_0_14260997_17157.c: In function 'check':
0_0_14260997_17157.c:11:5: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
     for (int i=0;x;x/=10)
     ^
0_0_14260997_17157.c:11:5: note: use option -std=c99, -std=gnu99, -std=c11 or -std=gnu11 to compile your code
0_0_14260997_17157.c: In function 'pre':
0_0_14260997_17157.c:18:5: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
     for (int i=1;i<=100000;i++)
     ^