第4章 习题解答

1、4.1 编写一个程序，输入A，B，C三个学生的考试分数，输出分数居中的那个学生名（A、B或C）及考试分数。#include int main() float a, b, c; printf(Please enter the score of A:n); scanf(%f, &a); printf(Please enter the score of B:n); scanf(%f, &b); printf(Please enter the score of C:n); scanf(%f, &c); if (a-b)*(a-c) = 0) printf(A gets the score %.1f,

2、a); else if (b-a)*(b-c) = 0) printf(B gets the score %.1f, b); else printf(C gets the score %.1f, c); return 0;4.2 编程求一元二次方程ax2+bx+c=0的根，系数a,b,c从终端输入。应考虑实根、复数根和无解的情况。#include#includeint main(void)float a, b, c, d, x1, x2;printf(Please key in 3 numbers:);scanf(%f%f%f, &a, &b, &c);if(a != 0)d = b*b -

3、4*a*c;if(d 0)x1 = (sqrt(d) - b) / (2*a);x2 = -(sqrt(d) + b) / (2*a);printf(Two real results:n%.6fn%.6fn, x1, x2);else if(d = 0)x1 = -b/(2*a);printf(One real result:n%.6fn, x1);elsex1 = -b/(2*a);x2 = sqrt(-d)/(2*a);printf(Two virsual results:n%.3f+%.3fin%.3f-%.3fin, x1, x2, x1, x2);else if(b != 0)x1

4、= -c/b;printf(One real result:n%.6fn, x1);else if(c!=0)printf(Error!No result.n);elseprintf(Anyone is result.n);return 0;4.3 输入一个日期（年、月、日），计算并输出该日期是这一年的第几天。switch方法：int main() int y, m, d, days; printf(Enter year:); scanf(%d, &y); printf(Enter month:); scanf(%d, &m); printf(Enter day:); scanf(%d, &d

5、); if(m12) printf(Input error!n); else days = d; switch(m) case 12: days += 30; case 11: days += 31; case 10: days += 30; case 9: days += 31; case 8: days += 31; case 7: days += 30; case 6: days += 31; case 5: days += 30; case 4: days += 31; case 3: days += (y%4=0 & y%100!=0 | y%400=0 ? 29 : 28); ca

6、se 2: days += 31; printf(%dn, days); return 0;函数方法：#include int mdays(int y, int m)if (m=2) return y%4=0 & y%100!=0 | y%400=0 ? 29 : 28;else if (m=4 | m=6 | m=9 | m=11) return 30;else return 31;int main()int y, m, d, days; printf(Enter year:); scanf(%d, &y); printf(Enter month:); scanf(%d, &m); prin

7、tf(Enter day:); scanf(%d, &d); if(m12 | dmdays(y, m) printf(Input error!n); else days = d; while(m1) days += mdays(y, m-1); m-; printf(%dn, days); return 0;4.4 假设工资税金按以下方法计算：x 1000元，不收取税金；1000x 2000，收取5%的税金；2000 x 3000，收取10%的税金；3000 x 4000，收取15%的税金；4000x5000，收取25%的税金。输入工资金额，输出应收取税金额度，要求分别用if语句和switc

8、h语句来实现。if方法：#include int main()float x = 0; printf(input the salary:); scanf(%f,&x); if(x0) printf(Input error!n); else if(x1000) printf(0.00n); else if(x2000) printf(%.2fn,x*0.05); else if(x3000) printf(%.2fn,x*0.1); else if(x4000) printf(%.2fn,x*0.15); else if(x5000) printf(%.2fn,x*0.2); else prin

9、tf(%.2fn,x*0.25); return 0;switch方法：#include int main() float x ; int xCase = 0; printf(input the salary:); scanf(%f,&x); if(x0) printf(Input error!n); else xCase = (int)(x/1000.0); switch(xCase) case 0: printf(0.00n); break; case 1: printf(%.2fn,x*0.05); break; case 2: printf(%.2fn,x*0.1); break; c

10、ase 3: printf(%.2fn,x*0.15); break; case 4: printf(%.2fn,x*0.2); break; default: printf(%.2fn,x*0.25); return 0;4.5 输入两个实数和一个四则运算符（+、-、*、/），根据运算符执行相应的运算并输出运算结果，分别用if语句和switch语句来实现。if方法：#includeint main(void)float a, b, result;char c;printf(Please key in 2 numbers:);scanf(%f%f, &a, &b);getchar();prin

11、tf(Please key in 1 operator:);scanf(%c, &c);if(c = +)result = a+b;printf(%f+%f=%.6fn, a, b, result);else if(c = -)result = a-b;printf(%f-%f=%.6fn, a, b, result);else if(c = *)result = a*b;printf(%f*%f=%.6fn, a, b, result);else if(c = /)if(b!=0)result = a/b;printf(%f/%f=%.6fn, a, b, result);elseprint

12、f(Error!No result.n);elseprintf(Error!No result.n);return 0;switch方法：#includeint main(void)float a, b, result;char c;printf(Please key in 2 numbers:);scanf(%f%f, &a, &b);getchar();printf(Please key in 1 operator:);scanf(%c, &c);switch(c)case +:result = a+b;printf(%f+%f=%.6fn, a, b, result);break;cas

13、e -:result = a-b;printf(%f-%f=%.6fn, a, b, result);break;case *:result = a*b;printf(%f*%f=%.6fn, a, b, result);break;case /:if(b!=0)result = a/b;printf(%f/%f=%.6fn, a, b, result);elseprintf(Error!No result.n);break;default:printf(Error!No result.n);return 0;4.6 统计输入正文中空格字符、制表符和换行符的个数。#includeint mai

14、n(void)int a = 0, b = 0, c = 0;int ch;while(ch=getchar() != EOF)if(ch = )a+;else if(ch = t)b+;else if(ch = n)c+;printf(The number of space, tab, enter is :%d, %d, %dn, a, b, c);return 0;4.7 编写一个程序，将输入的一行字符复制到输出，复制过程中将一个以上的空格字符用一个空格代替。#include int main() char c; int flag = 0; do c = getchar(); if(c!=

15、 ) putchar(c); flag = 0; else if(!flag) putchar(c); flag = 1; while(c != n); return 0;4.8 将输入的正文复制到输出，复制过程中删去每个输入行的前导空格。#includeint main(void)int ch, flag, i=0;char s800;while(ch=getchar() != EOF & i =20，每行输出8个数。计算公式为：a1=1,a2=1,an=an-1+an-2(n3)。#includeint main(void)int n, i, fib100;printf(Please ke

16、y in a number:);scanf(%d, &n);fib0 = 1;printf(%6d, fib0);fib1 = 1;printf(%6d, fib1);for(i=2; in; i+)fibi = fibi-1 + fibi-2;printf(%6d, fibi);if(i+1)%8 = 0)putchar(n);return 0;4.11 编写一个程序，输入两个整数，求它们的最大公约数和最小公倍数。#includeint main() int a,b,num1,num2,temp; printf(Input a & b:); scanf(%d%d,&num1,&num2);

17、a=num1; b=num2; if(ab) temp=a; a=b; b=temp; while(b!=0) temp=a%b; a=b; b=temp; printf(The GCD of %d and %d is: %dn,num1,num2,a); printf(The LCM of them is: %dn,num1*num2/a); return 0;4.12 输入两个整数，判断它们是否为互质数并输出判断结果。/*公因数只有1的两个非零自然数,叫做互质数。举例：2和3，公因数只有1，为互质数*/#includeint main(void)int m, n, i, min;print

18、f(Please key in two number:);scanf(%d%d, &m, &n);min = mn ? n : m;for(i=2; imin)printf(Yesn);elseprintf(Falsen);return 0;4.13 编写一个程序，验证哥德巴赫猜想：任何充分大（=4）的偶数都可以用两个素数之和表示，将4100中所有偶数分别用两个素数之和的形式输出。（例如：4=2+2,100=3+97）#include #include int Primes(int x); /判断素数函数int main() int i;int num; for(num=4;num=100;num+=2) for(i=1;i=num/2;i+) if(Primes(i) & Primes(num-i) printf(%d