如何在if語句中的條件內創建宏

Question

我需要遍歷嵌套在while循環內的for循環，以獲得幾種不同的條件。

每個語句的代碼的唯一更改是要應用的比較條件。

原來我複製粘貼所有的代碼多次，並改變大於符號的方向。

例如：

if (direction.horizontal == UIScrollDirectionLeft) { 
    int column = startColumn+1; 
    while (column < maxAllowed) { 
     for (int row = minRow; row < maxRow; row++) { 
      repeated code 
     } 
     column++; 
} else { 
    int column = minColumn -1; 
    while (column >= 0) { 
     for (int row = minRow; row < maxRow; row++) { 
      repeated code 
     } 
     column--; 
    } 
} 

是否有可能做條件運算符宏以便於代碼重用？

我真的很喜歡的東西可能是這樣的：

int startColumn = (direction.horizontal == UIScrollDirectionLeft) ? (startColumn+1) : minColumn -1; 
SignOfOperator theSignInTheWhile = (direction.horizontal == UIScrollDirectionLeft) ? "<" : ">="; 
int conditionToTestInWhile = (direction.horizontal == UIScrollDirectionLeft) ? maxAllowed : 0; 

while(startColumn,theSignInTheWhile,conditionToTestInWhile) { 
    // repeated code 
} 

我有另外4個情況下，像上面的一個...

Answer 1

你只需要一次循環代碼。只需更改步驟值和終止值。例如：

int start_column, end_column, column_step; 
    : 
switch (direction.horizontal) { 
    case UIScrollDirectionLeft: 
    column = start_column + 1; 
    column_step = 1; 
    end_column = max_allowed; 
    break; 
    case UIScrollDirectionRight: 
    column = min_column - 1; 
    column_step = -1; 
    end_column = -1; 
    break; 
    : 
} 
while (column != end_column) { 
    for (int row = minRow; row < maxRow; row++) { 
    repeated_code(); 
    } 
    column += column_step; 
}