如何解决C 多项式加法练习
我目前正在做算法课的练习。我被要求编写一个 C 程序，将用户输入的两个多项式相加，我可以通过询问用户每个多项式的最高次数及其系数来实现。
问题是用户的输入必须是例如-5x4+2x2+6（所有系数和度数都可以从0到9）。
我设法将此字符串转换为数组
void tableau(char *chaine) {
int i = 0;
while (1) {
scanf("%c",&chaine[i]);
if (chaine[i] == '\n') {
break;
} else {
i++;
}
}
}
我创建了一个结构
struct polynome {
int coeff;
int degre;
};
我找不到将这个数组转换为多项式的方法，这里是我编写的所有函数以使其工作，但我总是得到奇怪的输出：
int DEGREMAXTAB(char TAB[]) {
int i = 0;
int degre0 = 0;
while (TAB[i] != '\0') {
if (TAB[i] == 'x' && (int)(TAB[i+1]) > degre0)
degre0 = (int)(TAB[i+1]);
i++;
}
return degre0; // it returns the right highest degree + 48 for some reason,I don't know
}
void tabpoly(char chaine[],int degre0,struct polynome polynome[]) {
int k = 1;
int i = 0,a = 0,b = 0;
while (chaine[i]) { // I am sorry,all of this is really messy,I just tried
if (chaine[i] == '\0')
break;
if (chaine[i] == '-') {
k = -1;
i++;
}
if (chaine[i] == '+') {
k = 1;
i++;
}
if (chaine[i] != 'x') {
a = k * ((int)(chaine[i]));
i++;
}
i++;
b = ((int)(chaine[i]));
polynome[degre0].coeff = a;
polynome[degre0].degre = b;
degre0++;
i++;
}
}
void afficher(struct polynome poly[],int degre0) { /* maybe something is wrong here too I
really can't find the issue except by tweaking everything and causing other issues */
int i = 0;
char signe;
for (i = degre0; i >= 0; i--) {
if (poly[i].coeff < 0) {
signe = '\0';
} else {
signe = '+';
}
printf("%c%dx%d",signe,poly[i].coeff,poly[i].degre);
}
}
到目前为止我的主要内容：
int main(int argc,const char *argv[]) {
struct polynome poly1[6]; // the maximum degree is 5
int deg1 = 0,i = 0;
char chainea[21];
printf("Entrez votre premier polynôme\n");
tableau(chainea);
while (chainea[i] != '\0') {
printf("%c",chainea[i]);
i++;
} // did this to check that there was no problem here
deg1 = DEGREMAXTAB(chainea);
printf("%d\n",deg1); // same,except that I must return deg1-48 and idk why
tabpoly(chainea,deg1,poly1);
afficher(poly1,deg1);
}
我知道我的代码可能真的很乱，对此我深表歉意，如果有人能帮我解决这个问题，我会很高兴。这是我输入示例中的输入时的输出。
Entrez votre premier polynôme
-5x4+2x2+6
-5x4+2x2+6
4
-101x4+0x0+0x0+0x0+0x1Program ended with exit code: 0
Entrez votre premier polynôme
2x2
2x2
2
+2x2+0x0+0x1Program ended with exit code: 0
非常感谢，我尽量提供尽可能多的信息。 :)
解决方法
我找到了一个解决方案，但度数显示为倒数；常数是第一项。指数用作多项式的次数。
#include <stdio.h>
struct poly {
int coef[9];
};
struct poly add(struct poly P1,struct poly P2) {
struct poly result;
for (int i = 0; i < 9; i++) {
result.coef[i] = P1.coef[i] + P2.coef[i];
}
return result;
}
void display(struct poly P) {
printf("%d + %dx",P.coef[0],P.coef[1]);
for (int i = 2; i < 9; i++) {
printf(" + %dx%d",P.coef[i],i);
}
printf("\n");
}
int main() {
struct poly p1,p2,result;
printf("Enter coefficients in order[Po 1]: ");
for (int i = 0; i < 9; i++) {
scanf("%d",&p1.coef[i]);
}
printf("Enter coefficients in order[Po 2]: ");
for (int i = 0; i < 9; i++) {
scanf("%d",&p2.coef[i]);
}
result = add(p1,p2);
printf("\nThe Result is ");
for (int i = 0; i < 9; i++) {
printf("%d ",result.coef[i]);
}
printf("\n");
display(result);
return 0;
}
@sadbro：你的回答有问题：
- 系数数组的长度应为 10，循环应运行到
i <= 9或i < 10。甚至更好：将MAX_POWER定义为9并在for循环的数组大小中使用它。 - 如果系数按升序输入，则输出循环应从最高指数向下迭代到
0。 - 不应打印具有
0系数的单项式。 - 您不应打印等于
1或-1的系数。 - 您应该打印没有前导
+的负系数。 - 更一般的做法是不在
display()中打印尾随换行符。
这是修改后的版本：
#include <stdio.h>
#define MAX_POWER 9
struct poly {
int coef[MAX_POWER + 1];
};
struct poly add(struct poly P1,struct poly P2) {
struct poly result;
for (int i = 0; i <= MAX_POWER; i++) {
result.coef[i] = P1.coef[i] + P2.coef[i];
}
return result;
}
// return the number of bytes printed
int display(struct poly P) {
int pos = 0;
for (int i = MAX_POWER; i >= 0; i--) {
int coefficient = P.coef[i];
const char *prefix = "";
if (coefficient != 0) {
if (pos) {
if (coefficient > 0) {
prefix = " + ";
} else {
prefix = " - ";
coefficient = -coefficient;
}
} else {
if (coefficient < 0) {
prefix = "-";
coefficient = -coefficient;
}
}
pos += printf("%s",prefix);
if (coefficient != 1) {
pos += printf("%d",coefficient);
}
if (i > 1) {
pos += printf("x%d",i);
} else
if (i == 1) {
pos += printf("x");
}
}
}
if (pos == 0) {
pos += printf("0");
}
return pos;
}
int main() {
struct poly p1,result;
printf("Enter coefficients in order[Po 1]: ");
for (int i = 0; i <= MAX_POWER; i++) {
if (scanf("%d",&p1.coef[i]) != 1)
return 1;
}
printf("Enter coefficients in order[Po 2]: ");
for (int i = 0; i <= MAX_POWER; i++) {
if (scanf("%d",&p2.coef[i]) != 1)
return 1;
}
result = add(p1,p2);
printf("\nThe Result is");
for (int i = 0; i <= MAX_POWER; i++) {
printf(" %d",result.coef[i]);
}
printf("\n");
display(result);
printf("\n");
return 0;
}
您的代码中存在多个问题：
- 您应该使用简单的
fgets()读取多项式，而不是使用scanf()一次读取一个字符。scanf()不是最好的工具。 - 获得
48偏移量的原因是数字是 ASCII 字符，而不是整数值。您必须减去'0'的值（作为 ASCII 中的值48）才能得到相应的数字。 - 当您访问
poly数组中超出最大索引值的元素时，您会遇到未定义的行为，因为偏移量为 48。您应该检查指数是否在适当的范围内。 - 您会得到随机值，因为
poly数组未初始化。
这是修改后的版本：
#include <stdio.h>
struct polynome {
int coeff;
int degre;
};
int degremaxtab(const char tab[]) {
int i,exp,max_exp = 0;
for (i = 0; tab[i] != '\0'; i++) {
if (tab[i] == 'x') {
i++;
if (tab[i] >= '0' && tab[i] <= '9') {
exp = tab[i] - '0';
} else {
exp = 1;
}
if (max_exp < exp) {
max_exp = exp;
}
}
}
return max_exp;
}
int skip_spaces(const char chaine[],int i) {
while (chaine[i] == ' ' || chaine[i] == '\t' || chaine[i] == '\n') {
i++;
}
return i;
}
/* return the maximum exponent in the polynomial */
int tabpoly(const char chaine[],struct polynome polynome[],int max_degree) {
int i,max_exp,sign,coeff,exp;
for (i = 0; i <= max_degree; i++) {
polynome[i].coeff = 0;
polynome[i].degre = i;
}
i = 0;
max_exp = 0;
while (chaine[i] != '\0') {
i = skip_spaces(chaine,i);
// get sign (allow +-)
sign = 1;
if (chaine[i] == '+') {
i++;
}
i = skip_spaces(chaine,i);
if (chaine[i] == '-') {
sign = -1;
i++;
}
i = skip_spaces(chaine,i);
if (chaine[i] >= '0' && chaine[i] <= '9') {
coeff = chaine[i] - '0';
i++;
} else {
coeff = 1;
}
if (chaine[i] == 'x') {
i++;
if (chaine[i] >= '0' && chaine[i] <= '9') {
exp = chaine[i] - '0';
i++;
} else {
exp = 1;
}
} else {
exp = 0;
}
i = skip_spaces(chaine,i);
// check for a complete term
if (chaine[i] != '\0' && chaine[i] != '+' && chaine[i] != '-')
return -2; // syntax error
if (exp > max_degree)
return -1; // exponent too large
if (max_exp < exp)
max_exp = exp;
polynome[exp].coeff += sign * coeff;
}
return max_exp;
}
void afficher(struct polynome poly[],int degre0) {
int i,pos;
/* simple output */
for (i = degre0; i >= 0; i--) {
printf("%+dx%d",poly[i].coeff,poly[i].degre);
}
printf("\n");
/* clean output */
pos = 0;
for (i = degre0; i >= 0; i--) {
int coeff = poly[i].coeff;
int degre = poly[i].degre;
if (coeff != 0) {
if (coeff > 0) {
if (pos > 0)
pos += printf("+");
if (coeff != 1 || degre == 0)
pos += printf("%d",coeff);
} else {
if (coeff != -1 || degre == 0)
pos += printf("%d",coeff);
else
pos += printf("-");
}
if (degre > 0) {
printf("x");
if (degre > 1)
pos += printf("%d",degre);
}
}
}
if (pos == 0) {
printf("0");
}
printf("\n");
}
int main(int argc,const char *argv[]) {
struct polynome poly1[6]; // the maximum degree is 5
char chainea[100];
int deg1;
printf("Entrez votre premier polynôme\n");
// read a full line from stdin
if (!fgets(chainea,sizeof(chainea),stdin))
return 1;
deg1 = degremaxtab(chainea);
printf("exposant maximum: %d\n",deg1);
deg1 = tabpoly(chainea,poly1,5);
if (deg1 < 0) {
if (deg1 == -1)
printf("exposant trop grand\n");
else
if (deg1 == -2)
printf("erreur de syntaxe\n");
else
printf("erreur\n");
} else {
afficher(poly1,deg1);
}
return 0;
}
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