View Compilation Error

0_0_13254224_7131.c: In function 'Sum':
0_0_13254224_7131.c:18:2: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
  for(int i = 0;i < k+1;i++)
  ^
0_0_13254224_7131.c:18:2: note: use option -std=c99, -std=gnu99, -std=c11 or -std=gnu11 to compile your code
0_0_13254224_7131.c:26:3: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
   for(int i = 0; i < k+1; i++)
   ^
0_0_13254224_7131.c:33:3: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
   for(int i = 0; i < k; i++)
   ^
0_0_13254224_7131.c: In function 'main':
0_0_13254224_7131.c:51:3: error: expected expression before '/' token
   //char *index[20] ;
   ^
0_0_13254224_7131.c:52:3: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
   for(int i = 0; i < n; i++)
   ^
0_0_13254224_7131.c:55:4: error: expected expression before '/' token
    //index[i] = Sum(a,b) ;
    ^