範例

void main( int argc, char* argv[]) {
for ( int i = 
0; i < argc; i++ ) {
if (! isalpha(argv[0]) ) {
cout << "Not a letter";
} else {
cout << "A letter";
}
}
}

解決方案
  1. 移除否定
  2. 切換 ifelse 部分

void main( int argc, char* argv[]) {
for ( int i = 
0; i < argc; i++ ) {
if ( isalpha(argv[0]) ) {
cout << "A letter";
} else {
cout << "Not a letter";
}
}
}