如何使用switch条件语句而不是if编写此程序？
#include <iostream>
using namespace std;
int main()
{
int i;
for (i = 1; i <= 100; i++) {
if ((i % 7 == 0) && (i > 0)) {
cout << i << endl;
}
}
return 0;
}
答案 0 :(得分：0)
听起来你对switch语句有点不熟悉。 switch语句类似于if-else语句，除了它不是布尔参数。所以基本上它问：告诉我的价值。然后针对每个案例（可能的结果），它都会采取后续行动。
所以你想问：告诉我数字的值，模数7.如果它是零，加一个计数器。如果是1，请执行。
因此，您的代码应具有以下通用结构：
$crypt->setData($encrypted);
$decrypted = $crypt->decrypt();
答案 1 :(得分：0)
您要查找的代码应如下所示：
#include <iostream> // this is for std::cin and std::cout (standard input and output)
using namespace std; // to shorten std::cout into cout
int main() {
cout << "multiples of 7 lower than 100 are:" << endl;
for ( int i=1 ; i<=100 ; i++ ) {
switch ( i%7 ) {
case 0: // this case 0 is similar to if ( i%7 == 0 )
cout << i << " ";
break;
default:
break;
}
}
cout << endl;
return 0;
}
输出将是：
multiples of 7 lower than 100 are:
7 14 21 28 35 42 49 56 63 70 77 84 91 98
答案 2 :(得分：0)
可以根据您的情况将if语句替换为switch/case语句。但是我认为您对在何处使用if和何处switch/case语句有一些误解。我建议您像在现实生活中一样使用此声明。
如果要检查条件，请使用if。例如：
if (a > b){...}或if (a == 7){...}或if (functionReturnsTrue()){...}
当您有一组条件并且该组中每个元素的逻辑都不同时，可以使用switch/case语句。例如：
enum HttpMethod {
GET,
POST,
PUT,
DELETE,
};
...
void handleHttpRequest(HttpRequest req)
{
...
switch(req.getHttpMethod())
{
case GET: handleGETRequest(req); break;
case POST: handlePOSTRequest(req); break;
case PUT: handlePUTRequest(req); break;
case DELETE: handleDELETERequest(req); break;
default: throw InvalidHttpMethod(); // in case when noone corresponds to the variable
}
}
当然，您可以使用if语句编写相同的语句，但是switch/case语句也具有一些编译效果。当您switch类型的变量enum时，如果不检查变量的所有可能流，则可能至少会收到编译器警告。
答案 3 :(得分：-1)
你在这里：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.IO;
using iTextSharp.text;
using iTextSharp.text.pdf;
public partial class CreatePDFFromScratch : System.Web.UI.Page
{
protected void btnCreatePDF_Click(object sender, EventArgs e)
{
// Create a Document object
var document = new Document(iTextSharp.text.PageSize.LETTER.Rotate(), 0f, 0f, 0f, 0f);
// Create a new PdfWrite object, writing the output to a MemoryStream
var output = new MemoryStream();
var writer = PdfWriter.GetInstance(document, output);
// Open the Document for writing
document.Open();
// First, create our fonts..
var titleFont = FontFactory.GetFont("Arial", 18, Font.BOLD);
var subTitleFont = FontFactory.GetFont("Arial", 14, Font.BOLD);
var boldTableFont = FontFactory.GetFont("Arial", 12, Font.BOLD);
var endingMessageFont = FontFactory.GetFont("Arial", 10, Font.ITALIC);
var bodyFont = FontFactory.GetFont("Arial", 12, Font.NORMAL);
// Add the "Northwind Traders Receipt" title
document.Add(new Paragraph("Northwind Traders Receipt", titleFont));
// Now add the "Thank you for shopping at Northwind Traders. Your order details are below." message
document.Add(new Paragraph("Thank you for shopping at Northwind Traders. Your order details are below.", bodyFont));
document.Add(Chunk.NEWLINE);
// Add the "Order Information" subtitle
document.Add(new Paragraph("Order Information", subTitleFont));
// Create the Order Information table
var orderInfoTable = new PdfPTable(2);
orderInfoTable.HorizontalAlignment = 0;
orderInfoTable.SpacingBefore = 10;
orderInfoTable.SpacingAfter = 10;
orderInfoTable.DefaultCell.Border = 0;
orderInfoTable.SetWidths(new int[] { 1, 4 });
orderInfoTable.AddCell(new Phrase("Order:", boldTableFont));
orderInfoTable.AddCell(txtOrderID.Text);
orderInfoTable.AddCell(new Phrase("Price:", boldTableFont));
orderInfoTable.AddCell(Convert.ToDecimal(txtTotalPrice.Text).ToString("c"));
document.Add(orderInfoTable);
// Add the "Items In Your Order" subtitle
document.Add(new Paragraph("Items In Your Order", subTitleFont));
// Create the Order Details table
var orderDetailsTable = new PdfPTable(3);
orderDetailsTable.HorizontalAlignment = 0;
orderDetailsTable.SpacingBefore = 10;
orderDetailsTable.SpacingAfter = 35;
orderDetailsTable.DefaultCell.Border = 0;
orderDetailsTable.AddCell(new Phrase("Item #:", boldTableFont));
orderDetailsTable.AddCell(new Phrase("Item Name:", boldTableFont));
orderDetailsTable.AddCell(new Phrase("Qty:", boldTableFont));
foreach (System.Web.UI.WebControls.ListItem item in cblItemsPurchased.Items)
if (item.Selected)
{
// Each CheckBoxList item has a value of ITEMNAME|ITEM#|QTY, so we split on | and pull these values out...
var pieces = item.Value.Split("|".ToCharArray());
orderDetailsTable.AddCell(pieces[1]);
orderDetailsTable.AddCell(pieces[0]);
orderDetailsTable.AddCell(pieces[2]);
}
document.Add(orderDetailsTable);
// Add ending message
var endingMessage = new Paragraph("Thank you for your business! If you have any questions about your order, please contact us at 800-555-NORTH.", endingMessageFont);
endingMessage.SetAlignment("Center");
document.Add(endingMessage);
document.Close();
Response.ContentType = "application/pdf";
Response.AddHeader("Content-Disposition", string.Format("inline;filename=Receipt-{0}.pdf", txtOrderID.Text));
///create background
Response.BinaryWrite(output.ToArray());
Response.Cache.SetCacheability(HttpCacheability.NoCache);
string imageFilePath = Server.MapPath(".") + "/images/1.jpg";
iTextSharp.text.Image jpg = iTextSharp.text.Image.GetInstance(imageFilePath);
Document pdfDoc = new Document(iTextSharp.text.PageSize.LETTER.Rotate(), 0, 0, 0, 0);
jpg.ScaleToFit(790, 777);
jpg.Alignment = iTextSharp.text.Image.UNDERLYING;
pdfDoc.Open();
pdfDoc.NewPage();
pdfDoc.Add(jpg);
pdfDoc.Close();
Response.Write(pdfDoc);
Response.End();
}
}