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这样写你看的更清楚：main(){int a=2,b=-1;c=2;if(a<b)if(b<0)c=0;elsec++;printf("%d\n",c)}最后的else就近原则，是第二if不成立时的选项。而运行时，第一个if不成立，所以后面就不运行，直接运行printf语句，输出2.void main() {int a=2,b=-1,c=2; if (a<b) if(b<0) c=0; else c+=1; printf("%d\n",c); }结果2，if的嵌套，意思是如果a<b并且b<0,才执行c=0。题意不满足，所以不执行，else于离着它最近的if配对，所以这个程序时一个大的if里面嵌套一个if—else语句。所以当a<b不成立时，不执行这个if else所以c直接输出}

输入三个整数x,y,z，请把这三个数由小到大输出。# include <stdio.h>
int main()
{
int x,y,z,t;
scanf("%d,%d,%d",&x,&y,&z);
if(x>y)
{
t=x; x=y; y=t;
}
if(x>z)
{
t=x; x=z; z=t;
}
if(y>z)
{
t=y; y=z; z=t;
}
printf("small to big: %d%d%d", x,y,z);
return 0;
}
判断2000-2500之间的闰年。# include <stdio.h>
int main()
{
int year;
printf("input year: ");
scanf("%d",&year);
while(year<2000
year>2500)
{
printf("您输入的数字不在范围内，请重新输入有效数字: ");
scanf("%d",&year);
}
fun(year);
return 0;
}
int fun(int year)
{
if((year%4==0) && (year%100!=0)
(year%400==0))
printf("%d是闰年",year);
else
printf("%d不是闰年",year);
return 0;
}
平方根# include<stdio.h>
# include<math.h>
float x1, x2, disc, p, q;
void big(float a, float b)
{
x1 = (-b + sqrt(disc)) / (2 * a);
x2 = (-b - sqrt(disc)) / (2 * a);
}
void zero(float a, float b)
{
x1 = x2 = (-b) / (2 * a);
}
void small(float a, float b)
{
p = (-b) / (2 * a);
q = sqrt(-disc) / (2 * a);
}
int main()
{
int a, b, c;
printf("请输入 a b c:");
scanf("%d,%d,%d", &a, &b, &c);
printf("表达式为: %d*x^2+%d*x+%d = 0\n", a, b, c);
disc = b*b - 4*a*c;
if (disc > 0)
{
big(a, b);
printf("disc>0的根为: x1=%f
x2=%f\n", x1, x2);
}
else if (disc == 0)
{
zero(a, b);
printf("disc==0的根为:x1=%f
x2=%f\n", x1, x2);
}
else
{
small(a, b);
printf("disc<0的根为:x1=%f+%f x2=%f-%f\n", p, q, p, q);
}
return 0;
}
九九乘法表。# include <stdio.h>
int main()
{
int i,j,result;
printf("\n");
for (i=1;i<10;i++)
{
for(j=1;j<10;j++)
{
result=i*j;
printf("%d*%d=%-3d",i,j,result);/*-3d表示左对齐，占3位*/
}
printf("\n");/*每一行后换行*/
}
return 0;
}
杨辉三角。# include <stdio.h>
int main()
{
int a[10][10],i,j;
for(i=0;i<10;i++)
{
for(j=0;j<=i;j++)
{
if(i==j
j==0)
a[i][j]=1;
else
a[i][j]=a[i-1][j-1]+a[i-1][j];
}
}
for(i=0;i<10;i++)
{
for(j=0;j<=i;j++)
{
printf("%5d",a[i][j]);
}
printf("\n");
}
return 0;
}
斐波那契数列。# include <stdio.h>
int main()
{
long f1,f2;
int i; f1=f2=1;
for(i=1;i<=20;i++)
{
printf("%12ld %12ld",f1,f2);
if(i%2==0)
printf("\n");
f1=f1+f2;
f2=f1+f2;
}
return 0;
}
判断100-200之间有多少个素数，并输出所有素数。# include <stdio.h>
int main()
{
int i,j,flag;
for(i=100;i<=200;i++)
{
flag=1;
for(j=2;j<i;j++)
{
if(i%j==0)
flag=0;
}
if(flag==1)
printf("%5d\n",i);
}
return 0;
}
一个数如果恰好等于它的因子之和，这个数就称为“完数”。例如6=1＋2＋3.编程找出1000以内的所有完数。# include<stdio.h>
void main()
{
int i, j, sum;
for (i = 2; i <= 1000; i++)
{
sum = 1;
for (j = 2; j <= i / 2; j++)
{
if (i % j == 0)
sum += j;
}
if (sum == i)
{
printf("%d its factors are 1, ", i);
for (j = 2; j <= i / 2; j++)
{
if (i % j == 0)
printf("%d, ", j);
}
printf("\n");
}
}
}
输入两个正整数m和n，求其最大公约数和最小公倍数。#include <stdio.h>
//两数相乘的积除以这两个数的最大公约数就是最小公倍数。
int main()
{
int num1,num2,m,n,t;
printf("请输入两个数: ");
scanf("%d,%d",&num1,&num2);
if(num1<num2)
{
t=num1;
num1=num2;
num2=t;
}
m=num1*num2;
n=num1%num2;
while(n!=0)
{
num1=num2;
num2=n;
n=num1%num2;
}
printf("最大公约数: %d\n",num2);
printf("最小公倍数: %d\n",m/num2);
return 0;
}
水仙花数。# include <stdio.h>
int main()
{
int a,b,c,i;
printf("水仙花数：");
for(i=100;i<1000;i++)
{
a=i/100;
b=i/10%10;
c=i%10;
if(100*a+10*b+c==a*a*a+b*b*b+c*c*c)
printf("%-5d",i);
}
return 0;
}
猴子吃桃问题。# include <stdio.h>
int main()
{
int day,x1,x2;
/*定义 day、x1、x2 3 个变量为基本整型*/
day=9;
x2=1;
while(day>0)
{
x1=(x2+1)*2;
/*第一天的桃子数是第二天桃子数加1后的2倍*/
x2=x1;
day--;
/*因为从后向前推所以天数递减*/
}
printf("the total is %d\n",x1);
/* 输出桃子的总数*/
return 0;
}
递归求n的阶乘（n!）。# include <stdio.h>
void main()
{
int fun(int n);
int n,y;
printf("input an int num: ");
scanf("%d",&n);
y=fun(n);
printf("%d!=%d",n,y);
}
int fun(int n)
{
int f;
if(n<0)
printf("n<0,data error");
else if(n==0
n==1)
f=1;
else
f=fun(n-1)*n;
return f;
}
输入10个数求出其中最大的数以及该数是第几个数，用打擂台算法实现。# include <stdio.h>
void main()
{
int max(int x, int y);
int a[10],m,n,i;
printf("input 10 num: ");
for(i=0;i<10;i++)
scanf("%d",&a[i]);
for(i=1,m=a[0],n=0;i<10;i++)
{
if(max(m,a[i])>m)
{
m=max(m,a[i]);
n=i;
}
}
printf("the max num: %d\nit is the %dth num.\n",m,n+1);
}
int max(int x,int y)
{
return (x>y?x:y);
}
回文数。# include <stdio.h>
int main()
{
int n,s,num,m=0;
printf("请输入一个正整数：");
scanf("%d",&num);
s = num;
while(s!=0)
{
n = s%10;
//n是s的末位数
m = m*10 +n; //把s的末位数放到m的末位
s = s/10;
//去掉末位数的新s
}
if (num == m)
printf("%d 是回文数\n", num);
else
printf("%d 不是回文数\n",num);
return 0;
}
将一个数组逆序输出。# include<stdio.h>
int main()
{
int i,t,a[5] = {1,2,3,4,5};
int begin = 0, end = 4;
printf("Before reverse order：");
for (i=0; i<5; i++)
printf("%d", a[i]);
printf("\n");
while (begin<end)
{
t = a[begin];
a[begin] = a[end];
a[end] = t;
begin++;
end--;
}
printf("After reverse order：");
for (i=0; i<5;i++)
printf("%d", a[i]);
printf("\n");
return 0;
}
编写一个函数,由实参传来一个字符串,统计此字符串中字母、数字、空格和其他字符的个数,在主函数中输人字符串以及输出上述的结果。#include<stdio.h>
int letter, num, space, others;
void CountStr(char str[])
{
int i;
for (i = 0; str[i] != '\0'; i++)
{
if ((str[i] >= 'a'&& str[i] <= 'z')
(str[i] >= 'A' && str[i] <= 'Z'))
letter++;
else if (str[i] >= '0' && str[i] <= '9')
num++;
else if (str[i] == ' ')
space++;
else
others++;
}
}
int main()
{
char text[80];
printf("input string:");
gets(text);
printf("string: %s\n", text);
CountStr(text);
printf("\nletter:%d\nnum:%d\nspace:%d\nothers:%d\n", letter, num, space, others);
return 0;
}
动态链表。# include <stdio.h>
# include <stdlib.h>
# define len sizeof(struct Student)
# define S struct Student
S
{
int num;
float score;
S *next;
};
int n;
S *creat()
{
S *head,*p1,*p2;
n=0;
p1=p2=malloc(len);
scanf("%d,%f",&p1->num,&p1->score);
head=NULL;
while(p1->num!=0)
{
n=n+1;
if(n==1) head=p1;
else p2->next=p1;
p2=p1;
p1=malloc(len);
scanf("%d,%f",&p1->num,&p1->score);
}
p2->next=NULL;
return head;
}
void print(S* head)
{
S *p;
printf("now,these %d records are: \n",n);
p=head;
if(head!=NULL)
do
{
printf("%d%5.1f\n",p->num,p->score);
p=p->next;
}while(p!=NULL);
}
int main()
{
S *head;
head=creat();
print(head);
return 0;
}
冒泡排序。# include <stdio.h>
void main()
{
int i,j,t,a[5]={5,4,1,2,3};
for(i=0;i<4;i++)
{
for(j=0;j<4-i;j++)
{
if(a[j]>a[j+1])
{
t=a[j];
a[j]=a[j+1];
a[j+1]=t;
}
}
}
for(i=0;i<5;i++)
printf("%3d",a[i]);
}
选择排序。# include <stdio.h>
void main()
{
int i,j,t,min;
int a[5]={2,4,1,5,3};
for(i=0;i<4;i++)
{
min=i;
for(j=i+1;j<5;j++)
if(a[j]<a[min])
min=j;
t=a[min];a[min]=a[i];a[i]=t;
}
for(i=0;i<5;i++)
printf("%d ",a[i]);
}
插入排序。# include <stdio.h>
void sort(int a[], int len)
{
int i,j,t;
for(i=1; i<len; i++)
{
t = a[i];
for(j=i-1;a[j]>t;j--) // > 升序 < 降序
{
a[j+1] = a[j];
}
a[j+1] = t;
}
}
int main()
{
int i,a[5] = {5,4,3,2,1};
sort(a,5);
for(i=0;i<5;i++)
printf("%d ",a[i]);
return 0;
}
}