[英]Confusion about calculator program
int getop(char s[])
{
int i = 0, c, next;
/* Skip whitespace */
while((s[0] = c = getch()) == ' ' || c == '\t')
;
s[1] = '\0';
/* Not a number but may contain a unary minus. */
if(!isdigit(c) && enter code herec != '.' && c != '-')
return c;
if(c == '-')
{
next = getch();
if(!isdigit(next) && next != '.')
return c;
c = next;
}
else
c = getch();
while(isdigit(s[++i] = c)) //HERE
c = getch();
if(c == '.') /* Collect fraction part. */
while(isdigit(s[++i] = c = getch()))
;
s[i] = '\0';
if(c != EOF)
ungetch(c);
return NUMBER;
};
what if there is no blank space or tab than what value will s[0] will initialize .......& what is the use of s[1]='\\0' 如果没有空格或制表符,那么s [0]将初始化什么值呢?.......&s [1] ='\\ 0'的用途是什么
what if there is no blank space or tab than what value will s[0] will intialize 如果没有空格或制表符,那么s [0]将初始化什么值呢?
The following loop will continue executing until getch()
returns a character that's neither a space nor a tab: 以下循环将继续执行,直到getch()
返回的字符既不是空格也不是制表符:
while((s[0] = c = getch()) == ' ' || c == '\t')
;
what is the use of s[1]='\\0' s [1] ='\\ 0'的用途是什么
It converts s
into a C string of length 1, the only character of which has been read by getch()
. 它将s
转换为长度为1的C字符串 ,该字符串的唯一字符已由getch()
读取。 The '\\0'
is the required NUL-terminator. '\\0'
是必需的NUL终止符。
while((s[0] = c = getch()) == ' ' || c == '\t')
Read character until its not a tab or space. 读取字符,直到没有制表符或空格为止。
s[1] = '\0';
Convert char array s to a proper string in C format (all strings in c must be terminated with a null byte, which is represented by '\\0'. 将char数组s转换为C格式的适当字符串(c中的所有字符串都必须以空字节结尾,该空字节由'\\ 0'表示)。
If there is no space or tab, you're stuck with an infinite loop. 如果没有空格或制表符,那么您将陷入无限循环。
s[1]='\\0' is a way of marking the end so functions like strlen() know when to stop reading through c strings. s [1] ='\\ 0'是标记结束的一种方式,因此strlen()之类的函数知道何时停止读取c字符串。 it's called "Null-Terminating" a string: http://chortle.ccsu.edu/assemblytutorial/Chapter-20/ass20_2.html 它称为“ Null-Terminated”字符串: http : //chortle.ccsu.edu/assemblytutorial/Chapter-20/ass20_2.html
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