objective-c - 已声明但未设置的变量评估为真？

Question

我用下面的代码做了一个简单的计算器。现在它完美地执行。然而，当我试图改变周围的事物时，它不起作用。我使用 BOOL 程序 来检查是否继续要求该人输入或完成该程序。

如果我将 while 语句的表达式更改为 (program) 并更改 YES/NO program 语句，为什么代码无法执行 while 中的操作？

// A simple printing calculator
{
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]
    Calculator *deskCalc = [[Calculator alloc] init];
    double value1;
    char operator        
    BOOL program;

    [deskCalc setAccumulator: 0];

    while (!program) {
    NSLog (@"Please type in your expression");
    scanf (" %lf %c", &value1, &operator);
    program = NO;

        if (operator == '+') {
            [deskCalc add: value1];
        }
        else if (operator == '-') {
            [deskCalc subtract: value1];
        }
        else if (operator == '*' || operator == 'x') {
            [deskCalc multiply: value1];
        }
        else if (operator == '/') {
            if (value1 == 0)
                NSLog (@"Division by zero!");
            else
                [deskCalc divide: value1];
        }
        else if (operator == 'S') {
            [deskCalc set: value1];
        }
        else if (operator == 'E') {
            [deskCalc accumulator];
            program = YES;
        }
        else {
            NSLog (@"Unknown operator");
        }
    }

    NSLog (@"The result is %f", [deskCalc accumulator]);

    [deskCalc release];

    [pool drain];
    return 0;
}

Answer 1

您还没有设置 program 的初始值，因此它默认为一个垃圾值，恰好 为非零值。

声明时设置program的初始值:

BOOL program = NO; // or YES, whichever is appropriate