C5, 5.1, 5.2

 

2009年6月2日

static 变量 P70
Chapter 5 - Pointers and Arrays

---

 Exercise 5-1

 Exercise 5-2

Exercise 5-1. As written, getint treats a + or - not followed by a digit as a valid
representation of zero. Fix it to push such a character back on the input.

修改前的代码：

#include<ctype.h>
#include<stdio.h>
int getint(int *pn){
    int c, sign;
    while(isspace(c = getc(stdin)))
        ;
    if(!isdigit(c) && c != EOF && c != '+' && c != '-'){
        ungetc(c, stdin);
        return 0;
    }
    sign = (c == '-') ? -1 : 1;
    if(c == '+' || c == '-')
        c = getc(stdin);
    for(*pn = 0; isdigit(c); c = getc(stdin))
        *pn = 10 * *pn + (c - '0');
    *pn *= sign;
    if(c != EOF)
        ungetc(c, stdin);
    return c;
}

int main(){
    int arr[] = {1, 2, 3, 4, 5};
    int n;
    for(n = 0; n < 5 && getint(&arr[n]) != EOF; n++)
        ;
}


在13、14行中间加上这句

if(!isdigit(c)){
  ungetc(c, stdin);
  return 0;
 }

修改后的代码：

#include<ctype.h>
#include<stdio.h>
int getint(int *pn){
    int c, sign;
    while(isspace(c = getc(stdin)))
        ;
    if(!isdigit(c) && c != EOF && c != '+' && c != '-'){
        ungetc(c, stdin);
        return 0;
    }
    sign = (c == '-') ? -1 : 1;
    if(c == '+' || c == '-')
        c = getc(stdin);
    if(!isdigit(c)){
        ungetc(c, stdin);
        return 0;
    }
    for(*pn = 0; isdigit(c); c = getc(stdin))
        *pn = 10 * *pn + (c - '0');
    *pn *= sign;
    if(c != EOF)
        ungetc(c, stdin);
    return c;
}

int main(){
    int arr[] = {1, 2, 3, 4, 5};
    int n;
    for(n = 0; n < 5 && getint(&arr[n]) != EOF; n++)
        ;
}


 

Exercise 5-2. Write getfloat, the floating-point analog of getint. What type does getfloat
return as its function value?

#include<stdio.h>
#include<ctype.h>

int getfloat(float *p){
    char ch;
    int sign;
    while(isspace(ch = getc(stdin)))
        ;
    if(!isdigit(ch) && ch != EOF && ch != '.' && ch != '+' && ch != '-'){
        ungetc(ch, stdin);
        return 0;
    }
    sign = (ch == '-') ? -1 : 1;
    if(ch == '+' || ch == '-')
        ch = getc(stdin);
    if(!isdigit(ch) && ch != '.'){
        ungetc(ch, stdin);
    }
    for(*p = 0; isdigit(ch); ch = getc(stdin))
        *p = *p * 10 + (ch - '0');
    if(ch == '.'){
        float tmp;
        ch = getc(stdin);
        for(tmp = 0.1; isdigit(ch); ch = getc(stdin)){
            *p += tmp * (ch - '0');
            tmp *= 0.1;
        }
    }
    *p *= sign;
    if(ch != EOF)
        ungetc(ch, stdin);
    return ch;
}

float arr[5] = {1.1, 2.2, 3.3, 4.4, 5.5};
int main(){
    int i, tmp;
    for(i = 0; i < 5 && (tmp = getfloat(arr + i)) && tmp != EOF; i ++)
        ;
}