近100个C语言基础算法案例（初级篇）

13、C语言解一元二次方程

源代码：

/* Program to find roots of a quadratic equation when coefficients are entered by user. */
/* Library function sqrt() computes the square root. */

#include <stdio.h>
#include <math.h> /* This is needed to use sqrt() function.*/
int main()
{
  float a, b, c, determinant, r1,r2, real, imag;
  printf("Enter coefficients a, b and c: ");
  scanf("%f%f%f",&a,&b,&c);
  determinant=b*b-4*a*c;
  if (determinant>0)
  {
      r1= (-b+sqrt(determinant))/(2*a);
      r2= (-b-sqrt(determinant))/(2*a);
      printf("Roots are: %.2f and %.2f",r1 , r2);
  }
  else if (determinant==0)
  {
    r1 = r2 = -b/(2*a);
    printf("Roots are: %.2f and %.2f", r1, r2);
  }
  else
  {
    real= -b/(2*a);
    imag = sqrt(-determinant)/(2*a);
    printf("Roots are: %.2f+%.2fi and %.2f-%.2fi", real, imag, real, imag);
  }
  return 0;
}

输出1：

Enter coefficients a, b and c: 2.3
4
5.6
Roots are: -0.87+1.30i and -0.87-1.30i

输出2：

Enter coefficients a, b and c: 4
1
0
Roots are: 0.00 and -0.25

14、C语言检查是否是闰年

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

对于任意正数n，阶乘指的是：

factorial = 1*2*3*4....n

如果数值是负数，那么阶乘就不存在。并且我们规定，0的阶乘就是1。

源代码：

/* C program to display factorial of an integer if user enters non-negative integer. */

#include <stdio.h>
int main()
{
    int n, count;
    unsigned long long int factorial=1;         
    printf("Enter an integer: ");
    scanf("%d",&n);
    if ( n< 0)
        printf("Error!!! Factorial of negative number doesn't exist.");
    else
    {
       for(count=1;count<=n;++count)    /* for loop terminates if count>n */
       {
          factorial*=count;              /* factorial=factorial*count */
       }
    printf("Factorial = %lu",factorial);
    }
    return 0;
}

输出1：

Enter an integer: -5
Error!!! Factorial of negative number doesn't exist.

输出2：

Enter an integer: 10
Factorial = 3628800

先介绍到这里，下一篇将分享更多的C语言基础算法，敬请期待。