if语句详细解释

Question

#include <stdio.h>

#include <stdlib.h> // ANSI C exit() prototype

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

{

    int ch;         // place to store each character as read

    FILE *fp;       // "file pointer" 

    long count = 0;

    if (argc != 2)

    {

        printf("Usage: %s filename\n", argv[0]);

        exit(1);

    }

    if ((fp = fopen(argv[1], "r")) == NULL)

    {

        printf("Can't open %s\n", argv[1]);

        exit(1);

    }

    while ((ch = getc(fp)) != EOF)

    {

       putc(ch,stdout);  // same as putchar(ch);

       count++;

    }

    fclose(fp);

    printf("File %s has %ld characters\n", argv[1], count);

    

    return 0;

}

求每个if 语句的详细解释 越详细越好

Answer 1

 if (argc != 2)   //如果argc 不等于2， 就执行以下代码， 如果等于2， 就跳过。    {        printf("Usage: %s filename\n", argv[0]);        exit(1);    }    if ((fp = fopen(argv[1], "r")) == NULL) // 如果打开文件返回值为NULL , 就是打开失败了，就执行以下代码，否则就跳过。    {        printf("Can't open %s\n", argv[1]);        exit(1);    }