View Compilation Error

0_0_17162010_7152.c: In function 'main':
0_0_17162010_7152.c:5:2: error: expected expression before '/' token
  //char s1[100]="ABCDEFGHIJKLMNOPQRSTUVWXYZ";
  ^
0_0_17162010_7152.c:6:5: error: expected expression before '/' token
     //char s2[100]="VWXYZABCDEFGHIJKLMNOPQRSTU";
     ^
0_0_17162010_7152.c:15:4: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
    for(int i=0;i<len;i++)
    ^
0_0_17162010_7152.c:15:4: note: use option -std=c99, -std=gnu99, -std=c11 or -std=gnu11 to compile your code