主要是用for循環來寫九九乘法表

1.左下角

#include <stdio.h>
int main()
{
    int i, j;
    for (i = 1; i < 10; i++)
    {

        for (j = 1; j <= i; j++)
        {

            printf("%d*%d=%-3d ", j, i, i * j);
        }
        printf("\n");
    }
    return 0;
}

2.等腰三角形

#include <stdio.h>
int main()
{
    int a = 0, b = 0, c = 0;

    for (a = 9; a >= 1; a--)
    {
        for (c = 0; c <= (8 - a) * 4; c++)
        {
            printf(" ");
        }
        for (b = 1; b <= a; b++)
            printf("%d*%d=%2d  ", a, b, a * b);
        printf("\n\n");
    }
    return 0;
}

3.左上角

#include <stdio.h>
int main()
{
    int i = 0, j = 0;
    for (i = 9; i >= 1; i--)
    {
        for (j = 1; j <= i; j++)
            printf("%d*%d=%-3d  ", i, j, i * j);

        printf("\n");
    }
    return 0;
}

4.右上角

#include <stdio.h>
int main()
{
    int i, j;
    for (i = 9; i > 0; i--)
    {
        for (j = 9; j > 0; j--)
        {
            if (i < j)
                printf("\t");
            else
                printf("%d*%d=%2d  ", j, i, i * j);
        }
        printf("\n");
    }
    return 0;
}

5.右下角

#include <stdio.h>
int main()
{
    int i = 0, j = 0;
    for (i = 1; i < 10; i++)
    {

        for (j = 9; j > 0; j--)
        {
            if (i >= j)
                printf("%d*%d=%-3d ", i, j, i * j);
            else
                printf("\t");
        }
        printf("\n");
    }

    return 0;
}