源代码：
/* C program to check whether a year is leap year or not using if else statement.*/
#include <stdio.h>
int main(){
int year;
printf("Enter a year: ");
scanf("%d",&year);
if(year%4 == 0)
{
if( year%100 == 0) /* Checking for a century year */
{
if ( year%400 == 0)
printf("%d is a leap year.", year);
else
printf("%d is not a leap year.", year);
}
else
printf("%d is a leap year.", year );
}
else
printf("%d is not a leap year.", year);
return 0;
}
输出1：
Enter year: 2000
2000 is a leap year.
输出2：
Enter year: 1900
1900 is not a leap year.
输出3：
Enter year: 2012
2012 is a leap year.
15、C语言检查一个数是正数、负数还是零
源代码：
#include <stdio.h>
int main()
{
float num;
printf("Enter a number: ");
scanf("%f",&num);
if (num<=0)
{
if (num==0)
printf("You entered zero.");
else
printf("%.2f is negative.",num);
}
else
printf("%.2f is positive.",num);
return 0;
}
也可以使用if-else语句
/* C programming code to check whether a number is negative or positive or zero using nested if...else statement. */
#include <stdio.h>
int main()
{
float num;
printf("Enter a number: ");
scanf("%f",&num);
if (num<0) /* Checking whether num is less than 0*/
printf("%.2f is negative.",num);
else if (num>0) /* Checking whether num is greater than zero*/
printf("%.2f is positive.",num);
else
printf("You entered zero.");
return 0;
}
输出1：
Enter a number: 12.3
12.30 is positive.
输出2：
Enter a number: -12.3
-12.30 is negative.
输出3：
Enter a number: 0
You entered zero.
16、C语言检查某字符串是不是字母
源代码：
/* C programming code to check whether a character is alphabet or not.*/
#include <stdio.h>
int main()
{
char c;
printf("Enter a character: ");
scanf("%c",&c);
if( (c>='a'&& c<='z') || (c>='A' && c<='Z'))
printf("%c is an alphabet.",c);
else
printf("%c is not an alphabet.",c);
return 0;
}
输出1：
Enter a character: *
* is not an alphabet
输出2：
Enter a character: K
K is an alphabet
17、C语言计算自然数的和
源代码：
/* This program is solved using while loop. */
#include <stdio.h>
int main()
{
int n, count, sum=0;
printf("Enter an integer: ");
scanf("%d",&n);
count=1;
while(count<=n) /* while loop terminates if count>n */
{
sum+=count; /* sum=sum+count */
++count;
}
printf("Sum = %d",sum);
return 0;
}
也可以使用for循环语句
/* This program is solve using for loop. */
#include <stdio.h>
int main()
{
int n, count, sum=0;
printf("Enter an integer: ");
scanf("%d",&n);
for(count=1;count<=n;++count) /* for loop terminates if count>n */
{
sum+=count; /* sum=sum+count */
}
printf("Sum = %d",sum);
return 0;
}
输出：
Enter an integer: 100
Sum = 5050
也可以通过if-else语句
/* This program displays error message when user enters negative number or 0 and displays the sum of natural numbers if user enters positive number. */
#include <stdio.h>
int main()
{
int n, count, sum=0;
printf("Enter an integer: ");
scanf("%d",&n);
if ( n<= 0)
printf("Error!!!!");
else
{
for(count=1;count<=n;++count) /* for loop terminates if count>n */
{
sum+=count; /* sum=sum+count */
}
printf("Sum = %d",sum);
}
return 0;
}
18、C语言计算阶乘