C与指针中一题需要统计质数个数，给的答案不是很详细，大致核对没有问题。在网上没找到统计专门区间的质数表。
以1000为间隔统计结果
The number of Primes between 0 to 1000 is 168
The number of Primes between 1000 to 2000 is 134
The number of Primes between 2000 to 3000 is 127
The number of Primes between 3000 to 4000 is 121
The number of Primes between 4000 to 5000 is 118
The number of Primes between 5000 to 6000 is 115
The number of Primes between 6000 to 7000 is 117
The number of Primes between 7000 to 8000 is 107
The number of Primes between 8000 to 9000 is 109
The number of Primes between 9000 to 10000 is 113
The number of Primes between 10000 to 11000 is 106
The number of Primes between 11000 to 12000 is 103
The number of Primes between 12000 to 13000 is 109
The number of Primes between 13000 to 14000 is 104
The number of Primes between 14000 to 15000 is 103
The number of Primes between 15000 to 16000 is 108
The number of Primes between 16000 to 17000 is 98
The number of Primes between 17000 to 18000 is 104
The number of Primes between 18000 to 19000 is 94
The number of Primes between 19000 to 20000 is 104
The number of Primes between 20000 to 21000 is 98
The number of Primes between 21000 to 22000 is 104
The number of Primes between 22000 to 23000 is 100
The number of Primes between 23000 to 24000 is 104
The number of Primes between 24000 to 25000 is 94
The number of Primes between 25000 to 26000 is 97
The number of Primes between 26000 to 27000 is 102
The number of Primes between 27000 to 28000 is 94
The number of Primes between 28000 to 29000 is 98
The number of Primes between 29000 to 30000 is 92
The number of Primes between 30000 to 31000 is 95
The number of Primes between 31000 to 32000 is 92
The number of Primes between 32000 to 33000 is 105
The number of Primes between 33000 to 34000 is 101
The number of Primes between 34000 to 35000 is 94
The number of Primes between 35000 to 36000 is 91
The number of Primes between 36000 to 37000 is 100
The number of Primes between 37000 to 38000 is 94
The number of Primes between 38000 to 39000 is 90
The number of Primes between 39000 to 40000 is 96
The number of Primes between 40000 to 41000 is 88
The number of Primes between 41000 to 42000 is 100
The number of Primes between 42000 to 43000 is 103
The number of Primes between 43000 to 44000 is 85
The number of Primes between 44000 to 45000 is 96
The number of Primes between 45000 to 46000 is 86
The number of Primes between 46000 to 47000 is 90
The number of Primes between 47000 to 48000 is 95
The number of Primes between 48000 to 49000 is 89
The number of Primes between 49000 to 50000 is 97
以10000为间隔
The number of Primes between 0 to 10000 is 1229
The number of Primes between 10000 to 20000 is 1033
The number of Primes between 20000 to 30000 is 983
The number of Primes between 30000 to 40000 is 958
The number of Primes between 40000 to 50000 is 929
The number of Primes between 50000 to 60000 is 924
The number of Primes between 60000 to 70000 is 879
The number of Primes between 70000 to 80000 is 901
The number of Primes between 80000 to 90000 is 877
The number of Primes between 90000 to 100000 is 879
100000为间隔
The number of Primes between 0 to 100000 is 9592
The number of Primes between 100000 to 200000 is 8391
The number of Primes between 200000 to 300000 is 8014
The number of Primes between 300000 to 400000 is 7863
The number of Primes between 400000 to 500000 is 7678
The number of Primes between 500000 to 600000 is 7559
The number of Primes between 600000 to 700000 is 7446
The number of Primes between 700000 to 800000 is 7407
The number of Primes between 800000 to 900000 is 7324
The number of Primes between 900000 to 1000000 is 7224
1000000为间隔
The number of Primes between 0 to 1000000 is 78498
The number of Primes between 1000000 to 2000000 is 70435
The number of Primes between 2000000 to 3000000 is 67882
The number of Primes between 3000000 to 4000000 is 66331
The number of Primes between 4000000 to 5000000 is 65366
The number of Primes between 5000000 to 6000000 is 64337
The number of Primes between 6000000 to 7000000 is 63799
The number of Primes between 7000000 to 8000000 is 63129
The number of Primes between 8000000 to 9000000 is 62712
The number of Primes between 9000000 to 10000000 is 62090
测试了下最多到30000000，再往后程序就跑不动了。用的是char型数组，应该是跟内存有关吧。有空测试下int型数组。
想到要将质数的统计结果保存下来时，觉得在屏幕打印后抄下来太蛋疼了，就想输出到文件后直接复制。但puts和putchar都不能输出参数到文件，就试了下printf。
先输入输出重定向到文件，
fp=freopen("test.txt","w",stdin);
还是输出到屏幕，怎么回事。
后来才发现是stdin没有改成stdout，wtf....
修改后成功用printf输出到文件。
