为什么我在调用具有相似名称的变量的函数时得到错误的结果？ [英] Why I am getting wrong result when calling a function with variables of similar name?
本文介绍了为什么我在调用具有相似名称的变量的函数时得到错误的结果？的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
亲爱的专家
我正在尝试使用基本的C命令解决karastooba乘法问题。我创建了一个函数来添加两个存储为字符串的数字。
void sum（a，b，c）将a + b分配给c。
当我单独使用此函数时，我能够获得任何输入的总和。但是当我在递归函数中使用它时，我得到了一些错误的结果。我在连续的步骤中调用了这个函数，但是我只得到一个函数调用的结果。让我感到惊讶的是，当我改变变量的名称时，我得到了完美的结果。变量名称会对程序有什么影响吗？
我用Code :: Block来做所有这些
我有什么试过：
Dear Expert
I am trying to solve karastooba multiplication using basic C commands. I have created a function to add two numbers which are stored as string.
void sum(a,b,c) will assign a+b to c.
I was able to get sum for any input when I used this function alone. But when I used this in recursive function i am getting some wrong results. I called this function in consecutive steps, but I am getting result only for one function call. What surprising me is that I got perfect result sometimes when I changed the name of variables. Will name of variable have any influence in program ?
I am doing all these with Code::Block
What I have tried:
#include<stdio.h>
#include<string.h>
void sum(char*,char*,char*);
void prod(char*,char*,char*);
void seperate(char *a,char *b, char *c, char *d, char *x, char *y);
void powercalculation(char*,char);
void difference(char*, char*,char*);
unsigned char pub=0;
int main()
{
char x[50],y[50],z[50];
gets(x);
gets(y);
prod(x,y,z);
puts(z);
return(0);
}
void prod(char *x, char *y, char *z)
{
char a[25],b[25],c[25],d[25],n;
char temp1[50],temp2[50],temp3[50],temp4[50],ac[50],bd[50];
if(strlen(x)>strlen(y))
n=strlen(x);
else
n=strlen(y);
if(strlen(x)==1||strlen(y)==1) //either of input is singlr digit
{
strcpy(temp1,"0");
strcpy(temp2,"0");
if(strlen(x)==1) //adding y , x[0] times
{
temp3[0]=x[0];
for(;temp3[0]>'0';temp3[0]--)
{
sum(temp1,y,temp2);
strcpy(temp1,temp2);
}
}
else //adding , y[0] times
{
temp3[0]=y[0];
for(;temp3[0]>'0';temp3[0]--)
{
sum(temp1,x,temp2);
strcpy(temp1,temp2);
}
}
strcpy(z,temp2); //copy result and return
return;
}
else
{
seperate(a,b,c,d,x,y); //deriving a,b,c,d from x and y
sum(a,b,temp1); //a+b
sum(c,d,temp2); //c+d
puts(temp1);
puts(temp2);
prod(temp1,temp2,temp3); //(a+b)*(c+d)
prod(a,c,ac); //a*c
prod(b,d,bd); //b*d
difference(temp3,ac,temp1); //(a+b)*(c+d)-ac
difference(temp1,bd,temp3); //(a+b)*(c+d)-ac-bd
powercalculation(temp2,(2*n)); //powercalculation return 10^(n/2), for n even, it returns n/2 zeros,
//Here argument is 2*n so returns n zeros
strcat(ac,temp2); //(10^n)*a*c
sum(ac,bd,temp2); //(10^n)ac+bd
powercalculation(temp3,(n));
if(n%2==0) //if n is even temp3 is n/2 number of zeros
strcat(temp1,temp3);
else
prod(temp1,temp3,temp4); //(10^n/2){(a+b)(c+d)-ac-bd}
sum(temp4,temp2,z);
return;
}
}
//function for difference of a and b to c. a should be higher than b
//if difference of two fifty digit number is two digit, difference string size will be 2, no duplicate zeros in MSB
void difference(char *a, char *b, char *c) //a should be higher
{
char temp[10],temp1,temp2,i,k;
temp1=strlen(a)-1;
temp2=strlen(b)-1;
for(i=0;temp2>=0;temp2--,temp1--,i++) //taking individual digit and subtracting, diffenrce is stored in reverse form, ie LSB in temp[0]
{
if(a[temp1]>=b[temp2])
temp[i]=a[temp1]-b[temp2]+48;
else //in case of borrow
{
temp[i]=a[temp1]+10-b[temp2]+48;
if(a[temp1-1]>48)
a[temp1-1]--;
else
{
for(k=temp1-2;a[k]=='0';k--);
a[k]--;
for(k+=1;k<=temp1-1;k++)
a[k]='9';
}
}
}
for(;temp1>=0;temp1--,i++) //if size of b is less
temp[i]=a[temp1];
for(i-=1;temp[i]=='0';i--); //removing zeros in MSB
for(k=0;i>=0;k++,i--) //reversing string
c[k]=temp[i];
if(k>0)
c[k]='\0';
else
strcpy(c,"0");
return;
}
//function to calculate power(10,n/2)
void powercalculation(char *a, char n) //to calculate 10^(n/2)
{
if(n%2==0) //it will return n/2 zeros
{
strcpy(a,"00000000000000000000000000000000000000000000000");
n/=2;
a[n+1]='\0';
}
else //return 10^(n/2)
{
strcpy(a,"31622776601683793319988935444327");//sqrt(10)=3.1622776601683793319988935444327
n/=2;
a[n+1]='\0';
}
return;
}
//function to seperate x,y into a,b,c,d
void seperate(char *a,char *b, char *c, char *d, char *x, char *y)
{
char n,l1,l2,i,j,k,m,flag;
l1=strlen(x);
l2=strlen(y);
if(l1>l2)
n=l1;
else
n=l2;
if(l1==l2) //size of both numbers same
if(n%2==0) //if size is even
{
a[n/2]=b[n/2]=c[n/2]=d[n/2]='\0';
for(i=n-1,j=(n/2)-1;i>=(n/2);i--,j--) //assigning x and y to a,b,c,d
{
a[j]=x[i-(n/2)];
b[j]=x[i];
c[j]=y[i-(n/2)];
d[j]=y[i];
}
}
else //if numbers are odd
{
a[n/2]=c[n/2]='\0';
b[(n/2)+1]=d[(n/2)+1]='\0';
b[n/2]=x[n-1];
d[n/2]=y[n-1];
for(i=n-2,j=(n/2)-1;j>=0;i--,j--)
{
a[j]=x[i-(n/2)];
b[j]=x[i];
c[j]=y[i-(n/2)];
d[j]=y[i];
}
}
else if(l1>l2) //if size of first string is higher than second
if(l1%2==0) //if size of first is even, since n in algorithm is the sizr of bigger string
{
k=l2-(l1/2)-1;
a[l1/2]=b[l1/2]=d[l1/2]=c[k+1]='\0';
flag=1;
for(i=l1-1,j=(l1/2)-1,m=l2-1;i>=(l1/2);m--,i--,j--,k--)
{
a[j]=x[i-(l1/2)];
b[j]=x[i];
if(flag==1)
if(l2<=l1/2)
{
flag=0;
strcpy(d,y);
strcpy(c,"0");
}
if(flag==1)
{
d[j]=y[m];
if(k>=0)
c[k]=y[m-(l1/2)];
}
}
}
else //if size of first string odd
{
a[l1/2]='\0';
b[(l1/2)+1]='\0';
b[l1/2]=x[l1-1];
k=l2-(l1/2)-2;
flag=1;
for(i=n-2,j=(n/2)-1,m=l2-2;j>=0;i--,j--,m--,k--)
{
a[j]=x[i-(n/2)];
b[j]=x[i];
if(flag==1)
if(l2<=(l1/2)+1)
{
flag=0;
strcpy(d,y);
strcpy(c,"0");
}
if(flag==1)
{
d[j]=y[m];
if(k>=0)
c[k]=y[m-(l1/2)];
}
}
if(flag==1)
{
d[(l1/2)+1]='\0';
d[l1/2]=y[l2-1];
c[l2-(l1/2)-1]='\0';
}
}
else //if second string is bigger than first
if(l2%2==0) //size of second string even
{
k=l1-(l2/2)-1;
c[l2/2]=d[l2/2]=b[l2/2]=a[k+1]='\0';
flag=1;
for(i=l2-1,j=(l2/2)-1,m=l1-1;i>=(l2/2);m--,i--,j--,k--)
{
c[j]=y[i-(l2/2)];
d[j]=y[i];
if(flag==1)
if(l1<=l2/2)
{
flag=0;
strcpy(b,x);
strcpy(a,"0");
}
if(flag==1)
{
b[j]=x[m];
if(k>=0)
a[k]=x[m-(l2/2)];
}
}
}
else //size of secomd string odd
{
c[l2/2]='\0';
d[(l2/2)+1]='\0';
d[l2/2]=y[l2-1];
k=l1-(l2/2)-2;
flag=1;
for(i=l2-2,j=(l2/2)-1,m=l1-2;j>=0;i--,j--,m--,k--)
{
c[j]=y[i-(l2/2)];
d[j]=y[i];
if(flag==1)
if(l1<=(l2/2)+1)
{
flag=0;
strcpy(b,x);
strcpy(a,"0");
}
if(flag==1)
{
b[j]=x[m];
if(k>=0)
a[k]=x[m-(l2/2)];
}
}
if(flag==1)
{
b[(l2/2)+1]='\0';
b[l2/2]=x[l1-1];
a[l1-(l2/2)-1]='\0';
}
}
return;
}
//function defenition for sum
//it will give a+b to c for any size of a and b
//no zero will be in MSB
void sum(char *a, char *b, char *c) //to find a+b=c
{
char temp1,temp2,flag=0,i;
temp1=strlen(a)-1; //index of LSB of a
temp2=strlen(b)-1; //index of LSB of b
if(temp1==temp2) //size of both string equal
{
c[temp1+2]='\0'; //size of c=temp1+1-->extra one for carry
for(;temp1>=0;temp1--) //adding individual characters
{
c[temp1+1]=a[temp1]+b[temp1]-48; //adding ASCII and subtract ASCII of '0' to get difference
if(flag==1) //flag=1 if there is carry from previoud addition; initially its 0
{
c[temp1+1]++; //existing carry is added and flag set to 0
flag=0;
}
if(c[temp1+1]>57) //in case addition exceeds 10, carry will be generated
{
c[temp1+1]-=10;
flag=1;
}
}
if(flag==1) //setting up MSB
c[0]=49;
else
{
for(i=0;i c[i]=c[i+1];
}
}
else if(temp1>temp2) //if size of first string is higher, follow similar steps
{
c[temp1+2]='\0';
for(;temp2>=0;temp1--,temp2--)
{
c[temp1+1]=a[temp1]+b[temp2]-48;
if(flag==1)
{
c[temp1+1]++;
flag=0;
}
if(c[temp1+1]>57)
{
c[temp1+1]-=10;
flag=1;
}
}
for(;temp1>=0;temp1--) //extra digits in first string is added
{
c[temp1+1]=a[temp1]+flag;
if(c[temp1+1]>57)
{
c[temp1+1]-=10;
flag=1;
}
else
flag=0;
}
if(flag==1)
c[0]='1';
else
for(i=0;i<strlen(c);i++)>
c[i]=c[i+1];
}
else //second one is higher
{
c[temp2+2]='\0';
for(;temp1>=0;temp1--,temp2--)
{
c[temp2+1]=a[temp1]+b[temp2]-48;
if(flag==1)
{
c[temp2+1]++;
flag=0;
}
if(c[temp2+1]>57)
{
c[temp2+1]-=10;
flag=1;
}
}
for(;temp2>=0;temp2--) //extra digits in first string is added
{
c[temp2+1]=b[temp2]+flag;
if(c[temp2+1]>57)
{
c[temp2+1]-=10;
flag=1;
}
else
flag=0;
}
if(flag==1)
c[0]='1';
else
for(i=0;i<strlen(c);i++)>
c[i]=c[i+1];
}
return;
}
推荐答案
您的主要问题是，您使用指针Complety不正确。指针是一些变量，它只指向具有该值的内存。这就像有人居住的地址。这里有一些指针的新手解释。
我认为你的算法是一些字符串操作，但不是 Karatsuba算法。如果你想这样做：为每个调用新变量声明并用实际值填充它们以避免指针有问题。
用于将字符串转换为数字您最好使用 __ttoi 。这不仅会更容易，而且可以避免指针问题。 ：-O
Your primary problem is, that you are using pointers complety incorrect. A pointer is some variable which only points to memory which has the value. It is like the address, where somebody resides. Here is some newbie explanation of pointers.
I think that your algorithm is some string manipulation but not a Karatsuba algorithm. If you want to do it this way: declare for every call new variables and fill them with actual values to avoid the pointer problematics.
For converting a string into a number you better use __ttoi. That would not only be easier, but avoid the pointer probelm. :-O
您应该学习尽快使用调试器。而不是猜测你的代码在做什么，现在是时候看到你的代码执行并确保它完成你期望的。
调试器允许你跟踪执行line by line, inspect variables and you will see that there is a point where it stop doing what you expect.
Debugger - Wikipedia, the free encyclopedia[^]
Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]
you will see your code perform and probably where it go wrong.
You should learn to use the debugger as soon as possible. Rather than guessing what your code is doing, It is time to see your code executing and ensuring that it does what you expect.
The debugger allow you to follow the execution line by line, inspect variables and you will see that there is a point where it stop doing what you expect.
Debugger - Wikipedia, the free encyclopedia[^]
Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]
you will see your code perform and probably where it go wrong.
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