Question

while(ans=='Y'||'y')
    {
     cout<<"--MENU--"<<endl;
     cout<<"1.Create a file"<<endl;
     cout<<"2.Display that file"<<endl;
     cout<<"3.Exit"<<endl;
     cout<<"Enter your choice-";
     cin>>ch;
        switch(ch)
     {
        case 1:create();//create and display functions are written above this, which are not required 
        break;
        case 2:display();
        break;
        case 3:exit(0);
     }
     cout<<"Do you want the menu again?(Y or y for Yes and anything else for a No)";
     cin>>ans;
   }

我的期望-当您在最后一行的'ans'中输入Y或y以外的任何其他字母时，该程序的控制应退出while循环并执行下一行。

Reality-它再次执行整个while循环。

问题-为什么？假设您在最后一行输入“ n”，则编译器应检查“ ans”是否包含字符“ Y”（或“ y”），然后退出while循环。

Answer 1

ans == 'Y' || ans == 'y'期间的条件始终为true。

它的精算应该是：ans=='Y'

它的编写方式仅评估ECSCluster: Type: AWS::ECS::Cluster Properties: ClusterName: !Ref EnvironmentName ECSAutoScalingGroup: DependsOn: ECSCluster Type: AWS::AutoScaling::AutoScalingGroup Properties: VPCZoneIdentifier: !Ref Subnets LaunchConfigurationName: !Ref ECSLaunchConfiguration MinSize: !Ref ClusterMinSize MaxSize: !Ref ClusterMaxSize DesiredCapacity: !Ref ClusterDesiredCapacity CreationPolicy: ResourceSignal: Timeout: PT15M UpdatePolicy: AutoScalingRollingUpdate: MinInstancesInService: 1 MaxBatchSize: 1 PauseTime: PT15M SuspendProcesses: - HealthCheck - ReplaceUnhealthy - AZRebalance - AlarmNotification - ScheduledActions WaitOnResourceSignals: true ScaleUpPolicy: Type: AWS::AutoScaling::ScalingPolicy Properties: AdjustmentType: ChangeInCapacity AutoScalingGroupName: !Ref ECSAutoScalingGroup Cooldown: '1' ScalingAdjustment: '1' MemoryReservationAlarmHigh: Type: AWS::CloudWatch::Alarm Properties: EvaluationPeriods: '2' Statistic: Average Threshold: '70' AlarmDescription: Alarm if Cluster Memory Reservation is too high Period: '60' AlarmActions: - Ref: ScaleUpPolicy Namespace: AWS/ECS Dimensions: - Name: ClusterName Value: !Ref ECSCluster ComparisonOperator: GreaterThanThreshold MetricName: MemoryReservation ScaleDownPolicy: Type: AWS::AutoScaling::ScalingPolicy Properties: AdjustmentType: ChangeInCapacity AutoScalingGroupName: !Ref ECSAutoScalingGroup Cooldown: '1' ScalingAdjustment: '-1' MemoryReservationAlarmLow: Type: AWS::CloudWatch::Alarm Properties: EvaluationPeriods: '2' Statistic: Average Threshold: '30' AlarmDescription: Alarm if Cluster Memory Reservation is too Low Period: '60' AlarmActions: - Ref: ScaleDownPolicy Namespace: AWS/ECS Dimensions: - Name: ClusterName Value: !Ref ECSCluster ComparisonOperator: LessThanThreshold MetricName: MemoryReservation ECSLaunchConfiguration: Type: AWS::AutoScaling::LaunchConfiguration Properties: KeyName: !If [IsProd, !Ref 'AWS::NoValue', !Ref KeyName] ImageId: !Ref ECSAMI InstanceType: !Ref InstanceType SecurityGroups: - !Ref SecurityGroup IamInstanceProfile: !Ref ECSInstanceProfile UserData: "Fn::Base64": !Sub | #!/bin/bash source /etc/profile.d/proxy.sh yum install -y https://s3.amazonaws.com/ec2-downloads-windows/SSMAgent/latest/linux_amd64/amazon-ssm-agent.rpm yum install -y https://s3.amazonaws.com/amazoncloudwatch-agent/amazon_linux/amd64/latest/amazon-cloudwatch-agent.rpm yum install -y aws-cfn-bootstrap hibagent cat >> /opt/aws/amazon-cloudwatch-agent/etc/common-config.toml <<EOF [proxy] http_proxy="${!http_proxy}" https_proxy="${!https_proxy}" no_proxy="${!no_proxy}" EOF /opt/aws/bin/cfn-init -v --region ${AWS::Region} --stack ${AWS::StackName} --resource ECSLaunchConfiguration /opt/aws/bin/cfn-signal -e $? --region ${AWS::Region} --stack ${AWS::StackName} --resource ECSAutoScalingGroup /usr/bin/enable-ec2-spot-hibernation Metadata: AWS::CloudFormation::Init: config: packages: yum: collectd: [] commands: 01_add_instance_to_cluster: command: !Sub echo ECS_CLUSTER=${ECSCluster} >> /etc/ecs/ecs.config 02_enable_cloudwatch_agent: command: !Sub /opt/aws/amazon-cloudwatch-agent/bin/amazon-cloudwatch-agent-ctl -a fetch-config -m ec2 -c ssm:${ECSCloudWatchParameter} -s files: /etc/cfn/cfn-hup.conf: mode: 000400 owner: root group: root content: !Sub | [main] stack=${AWS::StackId} region=${AWS::Region} /etc/cfn/hooks.d/cfn-auto-reloader.conf: content: !Sub | [cfn-auto-reloader-hook] triggers=post.update path=Resources.ECSLaunchConfiguration.Metadata.AWS::CloudFormation::Init action=/opt/aws/bin/cfn-init -v --region ${AWS::Region} --stack ${AWS::StackName} --resource ECSLaunchConfiguration services: sysvinit: cfn-hup: enabled: true ensureRunning: true files: - /etc/cfn/cfn-hup.conf - /etc/cfn/hooks.d/cfn-auto-reloader.conf # This IAM Role is attached to all of the ECS hosts. It is based on the default role # published here: # http://docs.aws.amazon.com/AmazonECS/latest/developerguide/instance_IAM_role.html # # You can add other IAM policy statements here to allow access from your ECS hosts # to other AWS services. Please note that this role will be used by ALL containers # running on the ECS host. ECSRole: Type: AWS::IAM::Role Properties: Path: / RoleName: !Sub ${EnvironmentName}-ECSRole-${AWS::Region} AssumeRolePolicyDocument: | { "Statement": [{ "Action": "sts:AssumeRole", "Effect": "Allow", "Principal": { "Service": "ec2.amazonaws.com" } }] } ManagedPolicyArns: - !Sub "arn:aws:iam::${AWS::AccountId}:policy/CSOPSRestrictionPolicy" - !Sub "arn:aws:iam::${AWS::AccountId}:policy/HIPIAMRestrictionPolicy" - !Sub "arn:aws:iam::${AWS::AccountId}:policy/HIPBasePolicy" - arn:aws:iam::aws:policy/service-role/AmazonEC2RoleforSSM - arn:aws:iam::aws:policy/CloudWatchAgentServerPolicy Policies: - PolicyName: ecs-service PolicyDocument: | { "Statement": [{ "Effect": "Allow", "Action": [ "ecs:CreateCluster", "ecs:DeregisterContainerInstance", "ecs:DiscoverPollEndpoint", "ecs:Poll", "ecs:RegisterContainerInstance", "ecs:StartTelemetrySession", "ecs:Submit*", "ecr:BatchCheckLayerAvailability", "ecr:BatchGetImage", "ecr:GetDownloadUrlForLayer", "ecr:GetAuthorizationToken" ], "Resource": "*" }] } ECSInstanceProfile: Type: AWS::IAM::InstanceProfile Properties: Path: / Roles: - !Ref ECSRole ECSServiceAutoScalingRole: Type: AWS::IAM::Role Properties: AssumeRolePolicyDocument: Version: "2012-10-17" Statement: Action: - "sts:AssumeRole" Effect: Allow Principal: Service: - application-autoscaling.amazonaws.com Path: / ManagedPolicyArns: - !Sub "arn:aws:iam::${AWS::AccountId}:policy/CSOPSRestrictionPolicy" - !Sub "arn:aws:iam::${AWS::AccountId}:policy/HIPIAMRestrictionPolicy" - !Sub "arn:aws:iam::${AWS::AccountId}:policy/HIPBasePolicy" Policies: - PolicyName: ecs-service-autoscaling PolicyDocument: Statement: Effect: Allow Action: - application-autoscaling:* - cloudwatch:DescribeAlarms - cloudwatch:PutMetricAlarm - ecs:DescribeServices - ecs:UpdateService Resource: "*" ECSCloudWatchParameter: Type: AWS::SSM::Parameter Properties: Description: CloudWatch Log configs for ECS cluster Name: !Sub AmazonCloudWatch-${ECSCluster}-ECS Type: String Value: !Sub | { "logs": { "force_flush_interval": 5, "logs_collected": { "files": { "collect_list": [ { "file_path": "/var/log/messages", "log_group_name": "${ECSCluster}/var/log/messages", "log_stream_name": "{instance_id}", "timestamp_format": "%b %d %H:%M:%S" }, { "file_path": "/var/log/dmesg", "log_group_name": "${ECSCluster}/var/log/dmesg", "log_stream_name": "{instance_id}" }, { "file_path": "/var/log/docker", "log_group_name": "${ECSCluster}/var/log/docker", "log_stream_name": "{instance_id}", "timestamp_format": "%Y-%m-%dT%H:%M:%S.%f" }, { "file_path": "/var/log/ecs/ecs-init.log", "log_group_name": "${ECSCluster}/var/log/ecs/ecs-init.log", "log_stream_name": "{instance_id}", "timestamp_format": "%Y-%m-%dT%H:%M:%SZ" }, { "file_path": "/var/log/ecs/ecs-agent.log.*", "log_group_name": "${ECSCluster}/var/log/ecs/ecs-agent.log", "log_stream_name": "{instance_id}", "timestamp_format": "%Y-%m-%dT%H:%M:%SZ" }, { "file_path": "/var/log/ecs/audit.log", "log_group_name": "${ECSCluster}/var/log/ecs/audit.log", "log_stream_name": "{instance_id}", "timestamp_format": "%Y-%m-%dT%H:%M:%SZ" } ] } } }, "metrics": { "append_dimensions": { "AutoScalingGroupName": "${!aws:AutoScalingGroupName}", "InstanceId": "${!aws:InstanceId}", "InstanceType": "${!aws:InstanceType}" }, "metrics_collected": { "collectd": { "metrics_aggregation_interval": 60 }, "disk": { "measurement": [ "used_percent" ], "metrics_collection_interval": 60, "resources": [ "/" ] }, "mem": { "measurement": [ "mem_used_percent" ], "metrics_collection_interval": 60 }, "statsd": { "metrics_aggregation_interval": 60, "metrics_collection_interval": 10, "service_address": ":8125" } } } } ECSClusterParameter: Type: AWS::SSM::Parameter Properties: Description: !Sub ${EnvironmentName} - ECS Cluster Name: !Sub /${EnvironmentName}/ecs-cluster Type: String Value: !Ref ECSCluster ECSServiceAutoScalingRoleParameter: Type: AWS::SSM::Parameter Properties: Description: !Sub ${EnvironmentName} - ECS Service ASG Role Name: !Sub /${EnvironmentName}/ecs-service-asg-role Type: String Value: !GetAtt ECSServiceAutoScalingRole.Arn的相等比较，然后执行逻辑或用y解释为true（C中的任何非0值都视为true），因此不论第一部分如何，始终将整个条件评估为true。我希望这是有道理的。

为什么即使不满足条件，编译器为什么还要再次执行while循环？

1 个答案: