Program:

#include<iostream>
using namespace std;
void main()
{  

	int currHours,currMins,hoursWait,minutesWait;
	int hrs,min;
	char ch;
	do
	{
      cout<<"Enter present Hours:";
	  cin>>currHours;
	  cout<<"Enter present minutes:";
	  cin>>currMins;	
 	  cout<<"Enterthe number of hours to wait:";
	  cin>>hoursWait;
	  cout<<"Enter the number of minutes to wait:";
	  cin>>minutesWait;
      hrs=currHours+hoursWait;
	  min=currMins+minutesWait;
	  if(min>=60)
	  {
		  hrs++;
		  min =min-60;
	  }
	  if(hrs>12)
	  {
         hrs=hrs%12;
		  cout<<"Time:"<<hrs<<":"<<min<<"PM"<<endl;
	  }
	  else
	  {
		  	  cout<<"Time:"<<hrs<<":"<<min<<"AM"<<endl;
	  }
		cout<<"Enter y or Y to continue...";
	  cin>>ch;
     }while(ch == 'y' || ch =='Y');
}

Output:

Enter present Hours:19
Enter present minutes:30
Enterthe number of hours to wait:20
Enter the number of minutes to wait:15
Time:3:45PM
Enter y or Y to continue...n