View Compilation Error

0_0_28120951_7857.cpp: In function 'int main()':
0_0_28120951_7857.cpp:8:1: error: 'flag' was not declared in this scope
 flag=1;
 ^
0_0_28120951_7857.cpp:12:29: error: expected primary-expression before '||' token
 if(str[j]>='a'&&str[j]<='z')||(str[j]>='A'&&str[j]<='Z')||(str[j]=='_'||(str[j]>='0'&&str[j]<='9')){flag=1;}
                             ^
0_0_28120951_7857.cpp:15:1: error: expected '}' before 'else'
 else{flag=0;}
 ^