几个经典的C语言算法及代码

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编排 | strongerHuang

微信公众号 | 嵌入式专栏

作者：码农网 – 小峰

链接：http://www.codeceo.com/article/10-c-interview-algorithm.html

算法是一个程序和软件的灵魂，作为一名优秀的程序员，只有对一些基础的算法有着全面的掌握，才会在设计程序和编写代码的过程中显得得心应手。

嵌入式专栏

1

计算Fibonacci数列

Fibonacci数列又称斐波那契数列，又称黄金分割数列，指的是这样一个数列：1、1、2、3、5、8、13、21。

C语言实现的代码如下：

/* Displaying Fibonacci sequence up to nth term where n is entered by user. */
#include <stdio.h>
int main()
{
  int count, n, t1=0, t2=1, display=0;
  printf("Enter number of terms: ");
  scanf("%d",&n);
  printf("Fibonacci Series: %d+%d+", t1, t2); /* Displaying first two terms */
  count=2;    /* count=2 because first two terms are already displayed. */
  while (count<n)  
  {
    display=t1+t2;
    t1=t2;
    t2=display;
    ++count;
    printf("%d+",display);
  }
  return 0;
}

结果输出：

Enter number of terms: 10
Fibonacci Series: 0+1+1+2+3+5+8+13+21+34+

嵌入式专栏

2

回文检查

源代码：

/* C program to check whether a number is palindrome or not */
#include <stdio.h>
int main()
{
  int n, reverse=0, rem,temp;
  printf("Enter an integer: ");
  scanf("%d", &n);
  temp=n;
  while(temp!=0)
  {
    rem=temp%10;
    reverse=reverse*10+rem;
    temp/=10;
  }  
/* Checking if number entered by user and it's reverse number is equal. */  
  if(reverse==n)  
    printf("%d is a palindrome.",n);
  else
    printf("%d is not a palindrome.",n);
  return 0;
}

结果输出：

Enter an integer: 12321
12321 is a palindrome.

嵌入式专栏

3

质数检查

注：1既不是质数也不是合数。

源代码：

/* C program to check whether a number is prime or not. */
#include <stdio.h>
int main()
{
  int n, i, flag=0;
  printf("Enter a positive integer: ");
  scanf("%d",&n);
  for(i=2;i<=n/2;++i)
  {
    if(n%i==0)
    {
      flag=1;
      break;
    }
  }
  if (flag==0)
    printf("%d is a prime number.",n);
  else
    printf("%d is not a prime number.",n);
  return 0;
}

结果输出：

Enter a positive integer: 29
29 is a prime number.

嵌入式专栏

4

打印金字塔和三角形

使用 * 建立三角形

*
* *
* * *
* * * *
* * * * *

源代码：

#include <stdio.h>
int main()
{
  int i,j,rows;
  printf("Enter the number of rows: ");
  scanf("%d",&rows);
  for(i=1;i<=rows;++i)
  {
    for(j=1;j<=i;++j)
    {
      printf("* ");
    }
    printf("\n");
  }
  return 0;
}

如下图所示使用数字打印半金字塔。

1
1 2
1 2 3
1 2 3 4
1 2 3 4 5

源代码：

#include <stdio.h>
int main()
{
  int i,j,rows;
  printf("Enter the number of rows: ");
  scanf("%d",&rows);
  for(i=1;i<=rows;++i)
  {
    for(j=1;j<=i;++j)
    {
       printf("%d ",j);
    }
    printf("\n");
  }
  return 0;
}

用 * 打印半金字塔：

* * * * *
* * * *
* * * 
* *
*

源代码：

#include <stdio.h>
int main()
{
  int i,j,rows;
  printf("Enter the number of rows: ");
  scanf("%d",&rows);
  for(i=rows;i>=1;--i)
  {
    for(j=1;j<=i;++j)
    {
       printf("* ");
      }
  printf("\n");
  }
  return 0;
}

用 * 打印金字塔

        *
      * * *
    * * * * *
  * * * * * * *
* * * * * * * * *

源代码：

#include <stdio.h>
int main()
{
  int i,space,rows,k=0;
  printf("Enter the number of rows: ");
  scanf("%d",&rows);
  for(i=1;i<=rows;++i)
  {
    for(space=1;space<=rows-i;++space)
    {
       printf("  ");
    }
    while(k!=2*i-1)
    {
       printf("* ");
       ++k;
    }
    k=0;
    printf("\n");
  }
  return 0;
}

嵌入式专栏

5

简单的加减乘除计算器

源代码：

/* Source code to create a simple calculator for addition, subtraction, multiplication and division using switch...case statement in C programming. */
# include <stdio.h>
int main()
{
  char o;
  float num1,num2;
  printf("Enter operator either + or - or * or divide : ");
  scanf("%c",&o);
  printf("Enter two operands: ");
  scanf("%f%f",&num1,&num2);
  switch(o) {
    case '+':
      printf("%.1f + %.1f = %.1f",num1, num2, num1+num2);
      break;
    case '-':
      printf("%.1f - %.1f = %.1f",num1, num2, num1-num2);
      break;
    case '*':
      printf("%.1f * %.1f = %.1f",num1, num2, num1*num2);
      break;
    case '/':
      printf("%.1f / %.1f = %.1f",num1, num2, num1/num2);
      break;
    default:
      /* If operator is other than +, -, * or /, error message is shown */
      printf("Error! operator is not correct");
      break;
  }
  return 0;
}

结果输出：

Enter operator either + or - or * or divide : -
Enter two operands: 3.4
8.4
3.4 - 8.4 = -5.0

嵌入式专栏

6

检查一个数能不能表示成两个质数之和

源代码：

#include <stdio.h>
int prime(int n);
int main()
{
  int n, i, flag=0;
  printf("Enter a positive integer: ");
  scanf("%d",&n);
  for(i=2; i<=n/2; ++i)
  {
    if (prime(i)!=0)
    {
      if ( prime(n-i)!=0)
      {
        printf("%d = %d + %d\n", n, i, n-i);
        flag=1;
      }
    }
  }
  if (flag==0)
    printf("%d can't be expressed as sum of two prime numbers.",n);
  return 0;
}

/* Function to check prime number */
int prime(int n)
{
  int i, flag=1;
  for(i=2; i<=n/2; ++i)
     if(n%i==0)
        flag=0;
  return flag;
}

结果输出：

Enter a positive integer: 34
34 = 3 + 31
34 = 5 + 29
34 = 11 + 23
34 = 17 + 17

嵌入式专栏

7

用递归的方式颠倒字符串

源代码：

/* Example to reverse a sentence entered by user without using strings. */
#include <stdio.h>
void Reverse();
int main()
{
  printf("Enter a sentence: ");
  Reverse();
  return 0;
}

void Reverse()
{
  char c;
  scanf("%c",&c);
  if( c != '\n')
  {
    Reverse();
    printf("%c",c);
  }
}

结果输出：

Enter a sentence: margorp emosewa
awesome program

嵌入式专栏

8

实现二进制与十进制之间的相互转换

源代码：

/* C programming source code to convert either binary to decimal or decimal to binary according to data entered by user. */
#include <stdio.h>
#include <math.h>
int binary_decimal(int n);
int decimal_binary(int n);
int main()
{
  int n;
  char c;
  printf("Instructions:\n");
  printf("1. Enter alphabet 'd' to convert binary to decimal.\n");
  printf("2. Enter alphabet 'b' to convert decimal to binary.\n");
  scanf("%c",&c);
  if (c =='d' || c == 'D')
  {
   printf("Enter a binary number: ");
   scanf("%d", &n);
   printf("%d in binary = %d in decimal", n, binary_decimal(n));
  }
  if (c =='b' || c == 'B')
  {
   printf("Enter a decimal number: ");
   scanf("%d", &n);
   printf("%d in decimal = %d in binary", n, decimal_binary(n));
  }
  return 0;
}

/* Function to convert decimal to binary.*/
int decimal_binary(int n)
{
  int rem, i=1, binary=0;
  while (n!=0)
  {
    rem=n%2;
    n/=2;
    binary+=rem*i;
    i*=10;
  }
  return binary;
}

/* Function to convert binary to decimal.*/
int binary_decimal(int n)
{
  int decimal=0, i=0, rem;
  while (n!=0)
  {
    rem = n%10;
    n/=10;
    decimal += rem*pow(2,i);
    ++i;
  }
  return decimal;
}

结果输出：

嵌入式专栏

9

使用多维数组实现两个矩阵的相加

源代码：

#include <stdio.h>
int main()
{
  int r,c,a[100][100],b[100][100],sum[100][100],i,j;
  printf("Enter number of rows (between 1 and 100): ");
  scanf("%d",&r);
  printf("Enter number of columns (between 1 and 100): ");
  scanf("%d",&c);
  printf("\nEnter elements of 1st matrix:\n");

  /* Storing elements of first matrix entered by user. */
  for(i=0;i<r;++i)
    for(j=0;j<c;++j)
    {
      printf("Enter element a%d%d: ",i+1,j+1);
      scanf("%d",&a[i][j]);
    }

  /* Storing elements of second matrix entered by user. */
  printf("Enter elements of 2nd matrix:\n");
  for(i=0;i<r;++i)
    for(j=0;j<c;++j)
    {
     printf("Enter element a%d%d: ",i+1,j+1);
     scanf("%d",&b[i][j]);
    }

  /*Adding Two matrices */
  for(i=0;i<r;++i)
    for(j=0;j<c;++j)
       sum[i][j]=a[i][j]+b[i][j];

  /* Displaying the resultant sum matrix. */
  printf("\nSum of two matrix is: \n\n");
  for(i=0;i<r;++i)
     for(j=0;j<c;++j)
     {
         printf("%d   ",sum[i][j]);
         if(j==c-1)
             printf("\n\n");
     }

  return 0;
}

结果输出：

嵌入式专栏

10

矩阵转置

源代码：

#include <stdio.h>
int main()
{
  int a[10][10], trans[10][10], r, c, i, j;
  printf("Enter rows and column of matrix: ");
  scanf("%d %d", &r, &c);

/* Storing element of matrix entered by user in array a[][]. */
  printf("\nEnter elements of matrix:\n");
  for(i=0; i<r; ++i)
  for(j=0; j<c; ++j)
  {
      printf("Enter elements a%d%d: ",i+1,j+1);
      scanf("%d",&a[i][j]);
  }

/* Displaying the matrix a[][] */
  printf("\nEntered Matrix: \n");
  for(i=0; i<r; ++i)
  for(j=0; j<c; ++j)
  {
    printf("%d  ",a[i][j]);
    if(j==c-1)
      printf("\n\n");
  }

/* Finding transpose of matrix a[][] and storing it in array trans[][]. */
  for(i=0; i<r; ++i)
  for(j=0; j<c; ++j)
  {
     trans[j][i]=a[i][j];
  }

/* Displaying the transpose,i.e, Displaying array trans[][]. */
  printf("\nTranspose of Matrix:\n");
  for(i=0; i<c; ++i)
  for(j=0; j<r; ++j)
  {
    printf("%d  ",trans[i][j]);
    if(j==r-1)
      printf("\n\n");
  }
  return 0;
}

结果输出：

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