Google script to dynamically addressing a cell in google sheet

I create code as follow

for (var i = 1; i <= numOfCopy-1; i++){
          
          var DestCell = "C" & String(22 + (i * 4) );
          SpreadsheetApp.getUi().alert(DestCell);
          spreadsheet.getRange(DestCell).activate();
          spreadsheet.getRange('C22:E25').copyTo(spreadsheet.getActiveRange(), SpreadsheetApp.CopyPasteType.PASTE_NORMAL, false);
        
        }

To allow copy and paste a range for number of times that defined by user.

I expect the line var DestCell = "C" & String(22 + (i * 4) );

Will construct dynamic destination cell address. But it returns 0.

So that line spreadsheet.getRange(DestCell).activate(); gives error message, "Range not found"

String concatenation in JavaScript

The issue within your code is that you are using & to combine strings, which is not a valid operator in JavaScript. Instead, you should use the + operator for string concatenation.

Try this modified code:

function myFunction() {
  var spreadsheet = SpreadsheetApp.getActiveSpreadsheet().getSheetByName('Sheet1');
  var numOfCopy = 3; // ensure that this is an integer not as string (e.g. "3")

  for (var i = 1; i <= numOfCopy - 1; i++) {
    var DestCell = "C" + String(22 + (i * 4));
    Logger.log("Destination cell:" + DestCell);
    Logger.log(typeof DestCell);
    SpreadsheetApp.getUi().alert(DestCell); 
    spreadsheet.getRange(DestCell).activate(); 
    spreadsheet.getRange('C22:E25').copyTo(spreadsheet.getActiveRange(),
    SpreadsheetApp.CopyPasteType.PASTE_NORMAL,false
    ); 
  }
}

Sample Output:

Reference:

• JS String concatination using +
• Use the Apps Script execution log
• JavaScript execution logs