linux_C一站学习--课后习题（一）简单函数；分支语句；深入理解函数

3.3 形参和实参

1、定义一个函数increment，它的作用是将传进来的参数加1，然后在main函数中用increment函数来增加变量的值：

void increment(int x){ x = x + 1;}int main(void){ int i = 1, j = 2; increment(i); /* now i becomes 2 */ increment(j); /* now j becomes 3 */ return 0;}

这个increment函数能奏效吗？为什么？

答：不能，因为在函数increment（）内部，是形参x自加1，并没有将x赋给i或j，而在函数increment()调用完后，函数的栈就自行释放，x就算自加1，也是被释放掉，所以该自加1就没有任何意义，注意：变量i,j和形参x是不同的量。

正确的做法：

#include <stdio.h>int increment(int x){x=x+1;return x;}int main(void){int i=1,j=2;i=increment(i);j=increment(j);printf("i=%d,j=%d\n",i,j);return 0;}

4.1 if语句

1、以下是程序段编译能通过，执行也不出错，但是执行结果不正确（根据第 3节“程序的调试”，这是一个语义错误），请分析一下哪里错了。还有，既然错了为什么编译能通过呢？

int x = -1;

if (x > 0);

printf("x is positive.\n");

错在if后面的条件表达式后多了个；号。能编译成功是因为这不是一个语义错误，而是一个逻辑错误。

4.2 if/else语句

1、写两个表达式，分别取整数x的个位和十位。

2、写一个函数，参数是整数x，功能是打印参数x的个位和十位。

解：个位u=a%10;

十位d=((a%100)-u)/10

 

/*Example: * please enter a integer: * 34 * the tens is 3,the units is 4. * *//*Type Contract * (number)->(string) * */#include <stdio.h>/*This programme will give the units and tens of the integer we enter*/int main(void){int a,u,d;/*int m=0;*/printf("please enter a integer.\n");scanf("%d",&a);u=a%10;d=((a%100)-u)/10; printf(" the tens is %d,the units is %d.\n",d,u);/*int i=0;for(i=0;;i++){if(a/(10^i)==0)m=i;printf("this number is a %d-digit integer.\n",m);break;}*/return 0;}

5.1 return语句

1、编写一个布尔函数int is_leap_year(int year)，判断参数year是不是闰年。如果某一年的年份能被4整除，但不能被100整除，那么这一年就是闰年，此外，能被400整除的年份也是闰年。

/*This program will determine whether a entered integer reprents a leap year. * If it can be devided by 4 but can't be devided by 100,it is a leap year; * besides, it can be devided by 400,it is also a leap year. * Also,this program will list the situation of whether it is a leap year from 1990 to 2020. * */#include <stdio.h>int is_leap_year(int year){if((year%4==0)&&(year%100!=0)){return 1;}else if(year%400==0){return 1;}elsereturn 0;}/*Function name:print_year * Input parameter: *   b:int,can only be 0 or 1,indecates the controlling expression *   intyear:int,represents the number of year we entered after the terminal has reminded us * Output:a string printed by c-function 'printf' * Function:print whether the year is a leap year * * */void print_year(int b,int intyear){if (b==0)        printf("%d is not a leap year.\n",intyear);elseprintf("%d is a leap year.\n",intyear);}int main(void){int a,b;printf("please enter an integer to judge whether it is a leap year.\n");scanf("%d",&a);b=is_leap_year(a);print_year(b,a);int i=1990;for(i=1990;i<=2020;i++){int b=is_leap_year(i);print_year(b,i);}return 0;}

 

5.3递归

1、编写递归函数求两个正整数a和b的最大公约数（GCD，GreatestCommon Divisor），使用Euclid算法：

1.如果a除以b能整除，则最大公约数是b。

2.否则，最大公约数等于b和a%b的最大公约数。

/* * This program will get the Greatest Common Divisor(GCD) of two positive integers, with the applying of Euclid arithmetic: * 1.If a devides b with no reminder,the GCD is a * 2.Else,GCD equles the GCD of b and (a%b) * */#include <stdio.h>int GCD(int a,int b){if(a%b==0)return b;else{int recurse=GCD(b,a%b);return recurse;}}int main(void){int n1,n2,gcd;printf("please enter 2 different integer.\n");scanf("%d%d",&n1,&n2);gcd=GCD(n1,n2);printf("The Greatest Common Divisor if %d and %d is %d.\n",n1,n2,gcd);return 0;}

 

 

2、编写递归函数求Fibonacci数列的第n项，这个数列是这样定义的：

fib(0)=1

fib(1)=1

fib(n)=fib(n-1)+fib(n-2)

 

/* *This program will find out the n th item of the Fibonacci Series.  fib(0)=1  fib(1)=1  fib(n)=fib(n-1)+fib(n-2)  What is Fibonacci Series?  every item,except the 1st and the 2nd, equals the summary of it's prvent two items.  1,1,2,3,5,8,13,21,34,33,89,144... * */#include <stdio.h>int fibonacci(int n){if(n==0)return 1;else if(n==1)return 1;else{int recurse1=fibonacci(n-1);int recurse2=fibonacci(n-2);int result=recurse1+recurse2;return result;}}int main(void){int a,b;printf("which item of the Fibonacci Series whould you like to know,please enter it.\n");scanf("%d",&a);b=fibonacci(a);printf("the %d .th item of Fibonacci Series is %d.\n",a,b);/*List the previous n items of the F series,n can be get from the keyboard*/int c;int i=1;printf("Would you like to get the previous n items of the Fibonacci Series?give us a number.\n");scanf("%d",&c);for(i=1;i<=c;i++){int d=fibonacci(i);printf("No.%d item is:%d.\n",i,d);}return 0;}