c - 值字符如何转换为整数？

Question

下面是程序的源代码，如果输入是97，则输出为

Please enter a number between 97 and 121:97

The 1st output is: a
The 2nd output is: a
The 3rd output is b
The 4th output is 97
--------------------------------

这个输出背后的逻辑是什么？整数如何转换为字符？是ASCII Chart ？

#include <stdio.h>
#include <conio.h>
int main () 
{
    int a;
    printf("\n%s enter a number between 97 and 121:" , "Please");
    scanf("%d", &a);
    printf("\nThe 1st outpit is: %c", a);
    printf("\nThe 2nd output is: %c" ,a++);
    printf("\nThe 3rd output is %c", a--);
    printf("\nThe 4th output is %d", a);
    return 0;
}

Answer 1

How is an integer converted into character?

让我们先看看“%d”。

printf("\nThe 4th output is %d", a);

此时

a 的值为 97。当 printf() 看到一个 "%d" 时，它期望看到一个 int 作为下一个参数 - 确实如此 - 很好。 值 97 会导致打印 2 个字符:'9' 和 '7'。

fprintf c
The int argument is converted to signed decimal in the style [−]dddd..
C11dr §7.21.6.1 8

<小时/>

现在“%c”。

printf("\nThe 1st outpit is: %c", a);

此时

a 的值为 97。当 printf() 看到 "%c" 时，它期望看到 int 作为下一个参数 - 这很好 - 很好。然后将int值转换为unsigned char，仍然是值97。然后“打印”97对应的字符。不过，这种对应关系是压倒性的ASCII对于值 0-127，因此会看到字符“a”。

..., the int argument is converted to an unsigned char, and the resulting character is written.