Google Script Spreadsheet function to iterate over all cells and insert the value 0 if the cell is blank

gistfile1.js

function zeroCells() {
  var ss=SpreadsheetApp.getActiveSpreadsheet();
  var sheet=ss.getSheets()[0];
  var selection=sheet.getDataRange();
  var columns=selection.getNumColumns();
  var rows=selection.getNumRows();
  for (var column=1; column < columns; column++) {
    for (var row=1; row < rows; row++) { 
      var cell=selection.getCell(row,column);
      if (cell.isBlank()) {
        cell.setValue(0);
      }
    }
  }
}

@moxventura is correct, because row and column indexes start at 1.

Thanx man,
Helped me to create a function to validate whether a string is present in sheet or not.
/* Searches for a string in a sheet*/ function searchString(stringToSearch,sheetName) { var sheet=SpreadsheetApp.getActiveSpreadsheet().getSheetByName(sheetName); var selection=sheet.getDataRange(); var columns=selection.getNumColumns(); var columnsnames = selection.getColumn() var rows=selection.getNumRows(); for (var column=1; column < columns; column++) { for (var row=1; row < rows; row++) { var cell=selection.getCell(row,column); if (cell.getValue() == stringToSearch ) { return true; } } } }