I have changed my question. I want to convert an NSString to an unsigned int. Why? Because I want to do parallel payment in PayPal. Below I have given my coding in which I want to convert the NSString to an unsigned int. My query is: //optional, set shippingEnabled to TRUE if you want to display shipping //options to the user, default: TRUE [PayPal getPayPalInst].shippingEnabled = TRUE; //optional, set dynamicAmountUpdateEnabled to TRUE if you want to compute //shipping and tax based on the user's address choice, default: FALSE [PayPal getPayPalInst].dynamicAmountUpdateEnabled = TRUE; //optional, choose who pays the fee, default: FEEPAYER_EACHRECEIVER [PayPal getPayPalInst].feePayer = FEEPAYER_EACHRECEIVER; //for a payment with multiple recipients, use a PayPalAdvancedPayment object PayPalAdvancedPayment *payment = [[PayPalAdvancedPayment alloc] init]; payment.paymentCurrency = @"USD"; // A payment note applied to all recipients. payment.memo = @"A Note applied to all recipients"; //receiverPaymentDetails is a list of PPReceiverPaymentDetails objects payment.receiverPaymentDetails = [NSMutableArray array]; NSArray *emailArray = [NSArray arrayWithObjects:@"[email protected]",@"[email protected]", nil]; for (int i = 1; i <= 2; i++) { PayPalReceiverPaymentDetails *details = [[PayPalReceiverPaymentDetails alloc] init]; // Customize the payment notes for one of the three recipient. if (i == 2) { details.description = [NSString stringWithFormat:@"Component %d", i]; } details.recipient = [NSString stringWithFormat:@"%@",[emailArray objectAtIndex:i-1]]; unsigned order; if (i==1) { order = [[feeArray objectAtIndex:0] unsignedIntValue]; } if (i==2) { order = [[amountArray objectAtIndex:0] unsignedIntValue]; } //subtotal of all items for this recipient, without tax and shipping details.subTotal = [NSDecimalNumber decimalNumberWithMantissa:order exponent:-4 isNegative:FALSE]; //invoiceData is a PayPalInvoiceData object which contains tax, shipping, and a list of PayPalInvoiceItem objects details.invoiceData = [[PayPalInvoiceData alloc] init]; //invoiceItems is a list of PayPalInvoiceItem objects //NOTE: sum of totalPrice for all items must equal details.subTotal //NOTE: example only shows a single item, but you can have more than one details.invoiceData.invoiceItems = [NSMutableArray array]; PayPalInvoiceItem *item = [[PayPalInvoiceItem alloc] init]; item.totalPrice = details.subTotal; [details.invoiceData.invoiceItems addObject:item]; [payment.receiverPaymentDetails addObject:details]; } [[PayPal getPayPalInst] advancedCheckoutWithPayment:payment]; Can anybody tell me how to do this conversion? Thanks and regards in advance.