这个程序应该是我在2004年写的
当时还只是一个读化工专业的大四学生
基本上对什么编程规范、什么算法，什么性能优化没什么了解
只是简单地用字符串模拟实现了
任意大整数的四则运算
现在看来当然很幼稚了
不过为保持原来面目，一直没改，留做纪念。
供有需要的朋友参考
敬请指教
1
//long integer operation , inclue addition,substracttion,multiplicaton
2//and division
3#include <stdio.h>
4#include <conio.h>
5#include <ctype.h>
6#include <string.h>
7#define MAX 1000
8#define MARK ('0'-1)
9
10//The Prototypes of the functions
11char* Initialiaze(char [],int);
12int Read(char [],char [],char * );
13int Print(char [],char [],char [],char []);
14int Calculate(char[],char[],char[],char []);
15char* Addition(char[],char[]);
16char* Substraction(char[],char[]);
17char* Multiplication(char[],char[]);
18char* Division(char[],char[]);
19char Div_per_bit(char [],int , char []);
20int Sub_per_bit(char [],char [],int *);
21int Copy(char [],int ,char []);
22int Compare(char [],char []);
23int Data_Process(char []);
24int Value(char);
25int Check(char []);
26int Compare(char [],char []);
27int Judge(int);
28int Convert(char [],char [],int);
29
30//The main function,calling Read , Calculate and Print function
31int main(void)
32
{ char a[MAX],b[MAX],c[2*MAX],action[MAX],ch='\t';
33
while (ch!=EOF)
34
{
35 clrscr();
36 Read(a,b,action);
37 if (Calculate(a,b,c,action))
38 Print(a,b,c,action);
39 ch=getchar();
40
}
41 return 0;
42
}
43//The check function check if the input number is legal
44int Check(char s[])
45{ int i;
46 if (strlen(s)==0)
47 return 0;
48 if (strlen(s)>=MAX)
49 return 0;
50
51 for (i=0; s[i]; i++)
52 if (!isdigit(s[i]))
53 return 0;
54 return 1;
55}
56//The Iniatilize function ,initialize the result number before calculation
57char* Initialize(char s[],int length)
58{ int i;
59 for (i=0; i<length; i++)
60 s[i]=MARK;
61 return s;
62
63}
64//The Read function,Read the operands and the operation
65int Read(char a[],char b[],char action[])
66{
67 printf("************This Program calculats two long integer action!************\n");
68 printf("Input long integer A,max length is %d:\n",MAX);
69 gets(a);
70 while (!Check(a))
71 { printf("Input error , Please input a correct value :\n");
72 gets(a);
73 }
74 printf("Iuput the operation over a & b \n");
75 printf("addition is '+' ,substraction is '-',multiplication is '*',division is '/'\n");
76 printf(" Warning:\n");
77 printf("If you do the division,A must bigger than B ,and B must not equal to zero !\n");
78 gets(action);
79 while ((Compare(action,"+")!=0) && (Compare(action,"-")!=0) && (Compare(action,"*")!=0) && (Compare(action,"/")!=0))
80 { printf("Input error , Please input a correct action :\n");
81 gets(action);
82 }
83 printf("Input long integer b,max length is %d:\n",MAX);
84 gets(b);
85 while (!Check(b))
86 { printf("Input error , Please input a correct value :\n");
87 gets(b);
88 }
89 return 1;
90}
91//The Calculate function,calling Addition,Substraction,Multiplication or Division function in accordance with the action
92int Calculate(char a[],char b[],char c[],char action[])
93{
94 if (Compare(action,"+")==0)
95 { strcpy(c,Addition(a,b));
96 return 1;
97 }
98 if (Compare(action,"-")==0)
99 { if ((Substraction(a,b))!=NULL)
100 strcpy(c,Substraction(a,b));
101 else
102 { strcpy(c,"-");
103 strcat(c,Substraction(b,a));
104 }
105 return 1;
106 }
107 if (Compare(action,"*")==0)
108 { strcpy(c,Multiplication(a,b));
109 return 1;
110 }
111
112 if (Compare(action,"/")==0)
113 { if ((Division(a,b))!=NULL)
114 strcpy(c,Division(a,b));
115 else
116 { printf("Press Ctrl-Z to end, Press Enter to recalculate!\n");
117 return 0;
118 }
119 return 1;
120 }
121
122}
123//The Print function , print the result
124int Print(char a[],char b[],char c[],char action[])
125{ printf("The result of \n%s \n%s \n%s \nis :\n",a,action,b);
126 puts(c);
127 printf("Press Ctrl-Z to end , Press Enter to recalculate..\n");
128 return 1;
129}
130//The Addition function , add two operands and return the result
131char* Addition(char a[],char b[])
132{ char c[2*MAX],d[2*MAX];
133 int i,j,k,a_length,b_length;
134 Initialize(c,2*MAX);
135 a_length=strlen(a);
136 b_length=strlen(b);
137 for (i=a_length-1,j=b_length-1,k=2*MAX-1; ( i>=0 || j>=0 ) ; i--,j--,k--)
138 { if ( i>=0 && j>=0 )
139 c[k]=Value(a[i])+Value(b[j])+'0';
140 else
141 if (i>=0 && j<0 )
142 c[k]=Value(a[i])+'0';
143 else
144 if ( i<0 && j>=0 )
145 c[k]=Value(b[j])+'0';
146 }
147 Data_Process(c);
148 Convert(c,d,2*MAX);
149 return d;
150}
151//The Substraction function , substract one operand from another operand , and return the result
152char* Substraction(char a[],char b[])
153{ char c[2*MAX],d[2*MAX];
154 int i,j,k,a_length,b_length,sub_result,symbol,flag[2*MAX]={0};
155 Initialize(c,2*MAX);
156 a_length=strlen(a);
157 b_length=strlen(b);
158 if (strcmp(a,b)==0)
159 return ("0");
160 for (i=a_length-1,j=b_length-1,k=2*MAX-1; ( i>=0 || j>=0 ) ; i--,j--,k--)
161 { sub_result=a[i]-b[j];
162 symbol=Judge(sub_result);
163 if (i>=1 && j>=0)
164 { if (flag[k]==0)
165 { if (a[i]>=b[j])
166 c[k]=sub_result+'0';
167 else
168 { c[k]=sub_result+10+'0';
169 flag[k-1]=1;
170 }
171 }
172 else
173 { if (a[i]-b[j]>=1)
174 c[k]=sub_result-1+'0';
175 else
176 { c[k]=sub_result+9+'0';
177 flag[k-1]=1;
178 }
179 }
180 }
181 else
182 if (i==0 && j<0)
183 {
184 if (flag[k]==0)
185 c[k]=a[i];
186 else
187 { if (a[i]==1)
188 ;
189 else
190 c[k]=a[i]-1;
191 }
192 }
193 else
194 { if ((i==0) && (j==0))
195 { if (flag[k]==0)
196 { switch (symbol)
197 { case 0: ;
198 break;
199 case 1: c[k]=sub_result+'0';
200 break;
201 case -1: return NULL;
202 break;
203 }
204 }
205 else
206 { switch (Judge(sub_result-1))
207 { case 0: ;
208 break;
209 case 1: c[k]=sub_result-1+'0';
210 break;
211 case -1: return NULL;
212