如何解决malloc多分配的空间 - 编程论坛

#2

兔先生2019-12-08 18:44

#include<stdio.h>
#include<stdlib.h>
#include<string.h>

char* addBinary(char* a, char* b) {
    int  i, k, j, len;
    int  c;
    c = 0;
    j = strlen(a);
    k = strlen(b);
    len = j > k ? j : k;
    char* res = (char*)malloc(sizeof(char) * (len + 2));
    res[len + 1] = '\0';
    i = len - 1;
    while (i >= 0)
    {
        if (j - 1 >= 0 && k - 1 >= 0) {
            if (a[j - 1] - '0' + b[k - 1] - '0' + c == 2)
            {
                res[i] = '0';
                c = 1;
            }
            else
            {
                res[i] = a[j - 1] - '0' + b[k - 1] - '0' + c;
                c = 0;
            }
        }
        if (j - 1 < 0)
        {
            if (b[k - 1] - '0' + c == 2)
            {
                res[i] = '0';
                c = 1;
            }
            else {
                res[i] = b[k - 1] - '0' + c;
                c = 0;
            }
        }
        if (k - 1 < 0)
        {
            if (a[j - 1] - '0' + c == 2)
            {
                res[i] = '0';
                c = 1;
            }
            else {
                res[i] = a[j - 1] - '0' + c;
                c = 0;
            }
        }
        i--, j--, k--;
    }
    if (c > 0)
        res[0] = '1';
    else
        (*res)++;
    return res;
}

int main()
{
    char a[10] = "110";
    char b[10] = "1001";
    char* res;
    int i = 0;
    printf("%s",addBinary(a, b));
}

完整版代码

#3

rjsp2019-12-08 19:25

程序代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char* add_binary( const char* a, const char* b )
{
    size_t alen = strlen(a);
    size_t blen = strlen(b);
    size_t clen = (alen<blen?blen:alen)+1;
    char* c = malloc( clen+1 );
    c[clen] = '\0';

    const char* pa = a+alen;
    const char* pb = b+blen;
    char* pc = c+clen;
    char* pd = pc-1;
    for( char carry=0; pa>a||pb>b||carry!=0; )
    {
        if( pa > a )
            carry += *--pa - '0';
        if( pb > b )
            carry += *--pb - '0';
        *--pc = carry%2 + '0';
        carry /= 2;

        if( *pc == '1' )
            pd = pc;
    }

    memmove( c, pd, c+clen-pd+1 );
    return c;
}

#include <assert.h>

void test( const char* a, const char* b, const char* c )
{
    char* result = add_binary( a, b );
    if( strcmp(result,c) != 0 )
        printf( "%s + %s = %s (shouled be %s)\n", a, b, result, c );
    free( result );
}

int main( void )
{
    test( "0", "0", "0" );
    test( "1", "1", "10" );
    test( "000", "00000", "0" );
    test( "001", "00001", "10" );
    test( "1111", "11", "10010" );
    test( "11", "1111", "10010" );
}

#4

兔先生2019-12-09 16:05

carry += *--pa - '0';
大佬能解释一下是怎么实现的吗？
if (c > 0)
        res[0] = '1';
    else
        (*res)++;
还有这是什么意思？