C语言学习2--1：九九乘法和多种交换变量值的方法

1，九九乘法

#include <stdio.h>

int main(void)
{
    int i, j;

    for (i = 1; i <= 9; i++)
    {
        for (j = 1; j <= i; j++)    
        {
            printf("%d x %d = %2d ", j, i, i * j);    
        }
        putchar('
');
    }

    return 0;
}

结果：

1 x 1 = 1

1 x 2 = 2 2 x 2 = 4

1 x 3 = 3 2 x 3 = 6 3 x 3 = 9

1 x 4 = 4 2 x 4 = 8 3 x 4 = 12 4 x 4 = 16

1 x 5 = 5 2 x 5 = 10 3 x 5 = 15 4 x 5 = 20 5 x 5 = 25

1 x 6 = 6 2 x 6 = 12 3 x 6 = 18 4 x 6 = 24 5 x 6 = 30 6 x 6 = 36

1 x 7 = 7 2 x 7 = 14 3 x 7 = 21 4 x 7 = 28 5 x 7 = 35 6 x 7 = 42 7 x 7 = 49

1 x 8 = 8 2 x 8 = 16 3 x 8 = 24 4 x 8 = 32 5 x 8 = 40 6 x 8 = 48 7 x 8 = 56 8 x 8 = 64

1 x 9 = 9 2 x 9 = 18 3 x 9 = 27 4 x 9 = 36 5 x 9 = 45 6 x 9 = 54 7 x 9 = 63 8 x 9 = 72 9 x 9 = 81

2，交换变量值的方法

#include <stdio.h>

int main(void)
{
    int a = 3, b = 5;

    printf("after 0 swap, a = %d, b = %d
", a, b);
    printf("------------------
");

    int t;
    t = a;
    a = b;
    b = t;
    printf("after 1 swap, a = %d, b = %d
", a, b);
    printf("------------------
");

    // a = a ^ b;
    // b = a ^ b; // a ^ b ^ b ==> a
    // a = a ^ b; // a ^ b ^ a ==> b
    a ^= b;
    b ^= a;
    a ^= b;
    printf("after 2 swap, a = %d, b = %d
", a, b);
    printf("------------------
");

    a = a + b;
    b = a - b; // a + b - b
    a = a - b; // a + b - a
    printf("after 3 swap, a = %d, b = %d
", a, b);
    printf("------------------
");

    return 0;
}

结果：

after 0 swap, a = 3, b = 5

------------------

after 1 swap, a = 5, b = 3

------------------

after 2 swap, a = 3, b = 5

------------------

after 3 swap, a = 5, b = 3

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