程序 1.txt

算法设计与分析源代码算法设计与分析源代码

/* multiply.c */ 
/* 11/20/2008 */ 
#define MAXLENGTH 1000 
#include <stdio.h> 
#include <string.h> 
 
void compute(char *a, char *b, char *c); 
 
void main(void) 
{ 
    char a[MAXLENGTH], b[MAXLENGTH], c[MAXLENGTH * 2]; 
 
    puts("Input multiplier :"); 
    gets(a); 
    puts("Input multiplicand :"); 
    gets(b); 
 
    compute(a, b, c); 
 
    puts("Answer :"); 
    puts(c); 
    getchar(); 
} 
 
void compute(char *a, char *b, char *c) 
{ 
    int i, j, m, n; 
    long sum, carry; 
 
    m = strlen(a) - 1; 
    n = strlen(b) - 1; 
    for (i = m; i >= 0; i--) 
        a[i] -= '0'; 
    for (i = n; i >= 0; i--) 
        b[i] -= '0'; 
    c[m + n + 2] = '\0'; 
 
    carry = 0; 
    for (i = m + n; i >= 0; i--)  /* i 为坐标和 */ 
    {
        sum = carry; 
 
        if ((j = i - m) < 0) 
            j = 0; 
        for ( ; j<=i && j<=n; j++) /* j 为纵坐标 */ 
            sum += a[i-j] * b[j]; /* 累计一组数的和 */ 
 
        c[i + 1] = sum % 10 + '0'; /* 算出保留的数字 */ 
        carry = sum / 10; /* 算出进位 */ 
 
    } 
 
    if ((c[0] = carry+'0') == '0') /* if no carry, */ 
        c[0] = '\040'; /* c[0] equals to space */ 
}