C :

#include<stdio.h>
#include<math.h>

int IsPrime(int n);

int main()
{
	int count = 0;
	int i;
	for(i = 1;count < 100003;i++)
	{
		if(IsPrime(i))
		{
			count++;
		}
	}
	printf("%d",i-1);
}
int IsPrime(int num)  
{  
    if (num == 2 || num == 3)  
	{  
        return 1;  
	}  
	if (num % 6 != 1 && num % 6 != 5)  
	{  
    	return 0;  
    }  
    for (int i = 5; i*i <= num; i += 6)  
    {  
        if (num % i == 0 || num % (i+2) == 0)  
	    {  
	        return 0;  
	    }  
    }  
	return 1;  
}

C++ :

#include<stdio.h>
#include<string.h>
#include<math.h>
const int M =1299745;
bool mark[M];
void Seive()
{
	memset(mark,1,sizeof(mark));
	mark[0] = mark[1] = 0;
	for(int i = 2;i <= sqrt(M);i++)
	{
		if(mark[i])
		{
			for(int j = i*i; j< M;j+=i)
				mark[j] = 0;
		}
	}
}
int main()
{
	Seive();
	int i,conter= 0;
	for(i = 0;i <= M;i++)
	{
		if(mark[i])
			conter++;
		if(conter == 100002)
		{
			printf("%d",i);
			break;
		}
			
	}
		
	return 0;
}