C语言编程char类型转换

#inlcude <stdio.h>

void func1(void)
{
    char a = 0x7F;
    unsigned char b = a;
    unsigned int c = a;

    printf ("a: %d(0x%x)\n", a, a); // a: 127(0x7f)
    printf ("b: %d(0x%x)\n", b, b); // b: 127(0x7f)
    printf ("c: %d(0x%x)\n", c, c); // c: 127(0x7f)
}

void func2(void)
{
    char a = 0x80;
    unsigned char b = a;
    unsigned int c = a;

    printf ("a: %d(0x%x)\n", a, a); // a: -128(0xffffff80)
    printf ("b: %d(0x%x)\n", b, b); // b: 128(0x80)
    printf ("c: %d(0x%x)\n", c, c); // c: -128(0xffffff80)
}

void func3(void)
{
    char a = 0xFF;
    unsigned char b = a;
    unsigned int c = a;

    printf ("a: %d(0x%x)\n", a, a); // a: -1(0xffffffff)
    printf ("b: %d(0x%x)\n", b, b); // 255(0xff)
    printf ("c: %d(0x%x)\n", c, c); // c: -1(0xffffffff)
}

int main(void)
{
    func1();
    func2();
    func3();

    return 0;
}