15-1.txt

c primer 部分习题答案

PE 15-1
 
/* pe15-1.c */
#include <stdio.h>
#include <stdbool.h>  // C99 -- otherwise use int
 
int bstr_to_dec(const char * str);
bool check_val(const char * str);
int main(void)
{
    char value[8* sizeof (int) + 1];
    
    printf("Enter a binary number with up to %d digits: ", 8 * sizeof(int));
    
    while (gets(value) && value[0] != '\0')
    {
        if (!check_val(value))
            puts("A binary number contains just 0s and 1s.");
        else
            printf("%s is %d\n", value, bstr_to_dec(value));
        puts("Enter next value:");
    }
    
    puts("Done");
    return 0;
}
 
int bstr_to_dec(const char * str)
{
    int val = 0;
    
    while (*str != '\0')
        val = 2 * val + (*str++ - '0');
    return val;
}
 
bool check_val(const char * str)
{
    bool valid = true;
    
    while (valid && *str != '\0')
    {
        if (*str != '0' && *str != '1')
            valid = false;
        ++str;
    }
    
    return valid;
}