1 題目

功能：哥德巴赫猜想 描述： 任一大于2的整數(shù)都可寫成兩個質(zhì)數(shù)之和 驗證從 3 到 50 之間所有數(shù)都是否可以寫成兩個素數(shù)之和

2 思路

1. 創(chuàng)建判斷是否為素數(shù)的函數(shù)
2. 從 3 到 50 循環(huán)判斷是否可以有 2 個素數(shù)加和

3 代碼

#include <stdio.h> 
#include <stdlib.h>

/**
功能：哥德巴赫猜想
描述：
  任一大于2的整數(shù)都可寫成兩個質(zhì)數(shù)之和
  驗證從 3 到 50 之間所有數(shù)都是否可以寫成兩個素數(shù)之和
**/

int ss(int i) {                         // 素數(shù)的判斷

    int j;
    if (i <= 1)                         // 小于1的數(shù)不是素數(shù)
        return 0;
    if (i == 2)                         // 2是素數(shù)
        return 1;
    for (j = 2; j < i; j++) {           // 對大于2的數(shù)進(jìn)行判斷
        if (i % j == 0)
            return 0;
        else if (i != j + 1)
            continue;
        else
            return 1;
    }
}

int main(int argc, char const *argv[]) { 

    int i, j, k, flag1, flag2, n = 0;
    for (i = 3; i <= 50; i++)
      for (k = 2; k <= i / 2; k++) {
          j = i - k;
          flag1 = ss(k);                    // 判斷拆分出的數(shù)是否是素數(shù)
          if (flag1) {
              flag2 = ss(j);
              if (flag2) {                  // 如果拆分出的兩個數(shù)均是素數(shù)則輸出
                  printf("%d = %d+%d,\t", i, k, j);
                  n++;
                  if (n % 5 == 0)
                      printf("\n");
              }
          }
      }
  printf("\n");
} 

示例結(jié)果：

$ gcc ex068.c -o demo
$ ./demo
4 = 2+2,  5 = 2+3,  6 = 3+3,  7 = 2+5,  8 = 3+5,
9 = 2+7,  10 = 3+7, 10 = 5+5, 12 = 5+7, 13 = 2+11,
14 = 3+11,  14 = 7+7, 15 = 2+13,  16 = 3+13,  16 = 5+11,
18 = 5+13,  18 = 7+11,  19 = 2+17,  20 = 3+17,  20 = 7+13,
21 = 2+19,  22 = 3+19,  22 = 5+17,  22 = 11+11, 24 = 5+19,
24 = 7+17,  24 = 11+13, 25 = 2+23,  26 = 3+23,  26 = 7+19,
26 = 13+13, 28 = 5+23,  28 = 11+17, 30 = 7+23,  30 = 11+19,
30 = 13+17, 31 = 2+29,  32 = 3+29,  32 = 13+19, 33 = 2+31,
34 = 3+31,  34 = 5+29,  34 = 11+23, 34 = 17+17, 36 = 5+31,
36 = 7+29,  36 = 13+23, 36 = 17+19, 38 = 7+31,  38 = 19+19,
39 = 2+37,  40 = 3+37,  40 = 11+29, 40 = 17+23, 42 = 5+37,
42 = 11+31, 42 = 13+29, 42 = 19+23, 43 = 2+41,  44 = 3+41,
44 = 7+37,  44 = 13+31, 45 = 2+43,  46 = 3+43,  46 = 5+41,
46 = 17+29, 46 = 23+23, 48 = 5+43,  48 = 7+41,  48 = 11+37,
48 = 17+31, 48 = 19+29, 49 = 2+47,  50 = 3+47,  50 = 7+43,
50 = 13+37, 50 = 19+31,