print prime numbers between 100 and 200

Prime numbers: have no other factors than 1 and itself

Here are several ways to write a program in C language to print the prime numbers between 100 and 200:

The first: use two for loops to achieve

#include<stdio.h>
#include<windows.h>
intmain()
{
	int i = 0;
	int count = 0;
	for (i = 100; i <= 200; i++)
	{
		int j = 2;
		for (j = 2; j <= i - 1; j++)
		{
			if (i%j == 0)
			{
				break;
			}
		}
		if (j == i)
		{
			count++;
			printf(" %d", i);
		}
	}
	printf("\ncount=%d", count);
	system("pause");
	return 0;
}

The second: because the even number has a factor of 2 in addition to 1 and itself, so exclude the even numbers between 100 and 200

#include<stdio.h>
#include<windows.h>
intmain()
{
	int i = 0;
	int count = 0;
	for (i = 101; i <= 200; i+=2)
	{
		int j = 2;
		for (j = 2; j <= i - 1; j++)
		{
			if (i%j == 0)
			{
				break;
			}
		}
		if (j == i)
		{
			count++;
			printf(" %d", i);
		}
	}
	printf("\ncount=%d", count);
	system("pause");
	return 0;
}

The third:

(i/2) is i divisible by 2

#include<stdio.h>
#include<windows.h>
intmain()
{
	int i = 0;
	int count = 0;
	for (i = 100; i <= 200; i++)
	{
		int j = 2;
		for (j = 2; j <= (i/2); j++)
		{
			if (i%j == 0)
			{
				break;
			}
		}
		if (j>(i/2))
		{
			count++;
			printf(" %d", i);
		}
	}
	printf("\ncount=%d", count);
	system("pause");
	return 0;
}

Fourth: Before synthesis, give optimization

Use square root sqrt in mathematics

#include<stdio.h>
#include<math.h>
#include<windows.h>
intmain()
{
	int i = 0;
	int count = 0;
	for (i = 101; i <= 200; i+=2)
	{
		int j = 0;
		for (j = 2; j <= sqrt(i); j++)
		{
			if (i%j == 0)
			{
				break;
			}
		}
		if (j>sqrt(i))
		{
			count++;
			printf(" %d", i);
		}
	}
	printf("\ncount=%d", count);
	system("pause");
	return 0;
}