# 近100个C语言基础算法案例（初级篇）

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下面这些C语言基础算法案例都是经过测试和验证过了的，欢迎各位使用。

本文是该系列的第一篇，都是一些相对初级的算法，很适合刚开始学C语言的同学。

## 1、C语言打印一条语句

源代码：

```/* C Program to print a sentence. */
#include <stdio.h>
int main()
{
printf("C Programming"); /* printf() prints the content inside quotation */
return 0;
}```

输出：

`C Programming`

## 2、C语言打印用户输入的一个整数

源代码：

```#include <stdio.h>
int main()
{
int num;
printf("Enter a integer: ");
scanf("%d",&num);  /* Storing a integer entered by user in variable num */
printf("You entered: %d",num);
return 0;
}```

输出：

```Enter a integer: 25
You entered: 25```

## 3、C语言实现两个整数相加

源代码：

```/*C programming source code to add and display the sum of two integers entered by user */

#include <stdio.h>
int main( )
{
int num1, num2, sum;
printf("Enter two integers: ");
scanf("%d %d",&num1,&num2); /* Stores the two integer entered by user in variable num1 and num2 */

sum=num1+num2;      /* Performs addition and stores it in variable sum */
printf("Sum: %d",sum);  /* Displays sum */
return 0;
}```

输出：

```Enter two integers: 12
11
Sum: 23```

## 4、C语言实现两个小数相乘

源代码：

```/*C program to multiply and display the product of two floating point numbers entered by user. */

#include <stdio.h>
int main( )
{
float num1, num2, product;
printf("Enter two numbers: ");
scanf("%f %f",&num1,&num2);        /* Stores the two floating point numbers entered by user in variable num1 and num2 respectively */
product = num1*num2;  /* Performs multiplication and stores it */
printf("Product: %f",product);
return 0;
}```

输出：

```Enter two numbers: 2.4
1.1
Product: 2.640000```

## 5、C语言查找字符的ASCII值

源代码：

```/* Source code to find ASCII value of a character entered by user */

#include <stdio.h>
int main(){
char c;
printf("Enter a character: ");
scanf("%c",&c);        /* Takes a character from user */
printf("ASCII value of %c = %d",c,c);
return 0;
}```

输出：

```Enter a character: G
ASCII value of G = 71```

## 6、C语言根据用户输入的整数做商和余数

源代码：

```/* C Program to compute remainder and quotient  */

#include <stdio.h>
int main(){
int dividend, divisor, quotient, remainder;
printf("Enter dividend: ");
scanf("%d",&dividend);
printf("Enter divisor: ");
scanf("%d",&divisor);
quotient=dividend/divisor;           /*  Computes quotient */
remainder=dividend%divisor;          /* Computes remainder */
printf("Quotient = %d\n",quotient);
printf("Remainder = %d",remainder);
return 0;
}```

输出：

```Enter dividend: 25
Enter divisor: 4
Quotient = 6
Remainder = 1```

## 7、C语言获取整型、单精度浮点型、双精度浮点型和字符型的长度

基本语法是：

```temp = sizeof(operand);
/* Here, temp is a variable of type integer,i.e, sizeof() operator
returns integer value. */```

源代码：

```/* This program computes the size of variable using sizeof operator.*/

#include <stdio.h>
int main(){
int a;
float b;
double c;
char d;
printf("Size of int: %d bytes\n",sizeof(a));
printf("Size of float: %d bytes\n",sizeof(b));
printf("Size of double: %d bytes\n",sizeof(c));
printf("Size of char: %d byte\n",sizeof(d));
return 0;
}```

输出：

```Size of int: 4 bytes
Size of float: 4 bytes
Size of double: 8 bytes
Size of char: 1 byte```

## 8、C语言获取关键字long的长度范围

源代码：

```#include <stdio.h>
int main(){
int a;
long int b;                /* int is optional. */
long long int c;            /* int is optional. */
printf("Size of int = %d bytes\n",sizeof(a));
printf("Size of long int = %ld bytes\n",sizeof(b));
printf("Size of long long int = %ld bytes",sizeof(c));
return 0;
}```

输出：

```Size of int = 4 bytes
Size of long int = 4 bytes
Size of long long int = 8 bytes```

## 9、C语言交换数值

源代码：

```#include <stdio.h>
int main(){
float a, b, temp;
printf("Enter value of a: ");
scanf("%f",&a);
printf("Enter value of b: ");
scanf("%f",&b);
temp = a;    /* Value of a is stored in variable temp */
a = b;       /* Value of b is stored in variable a */
b = temp;    /* Value of temp(which contains initial value of a) is stored in variable b*/
printf("\nAfter swapping, value of a = %.2f\n", a);
printf("After swapping, value of b = %.2f", b);
return 0;
}```

输出：

```Enter value of a: 1.20
Enter value of b: 2.45

After swapping, value of a = 2.45
After swapping, value of b = 1.2```

## 10、C语言检查数值是奇数还是偶数

源代码：

```/*C program to check whether a number entered by user is even or odd. */

#include <stdio.h>
int main(){
int num;
printf("Enter an integer you want to check: ");
scanf("%d",&num);
if((num%2)==0)      /* Checking whether remainder is 0 or not. */
printf("%d is even.",num);
else
printf("%d is odd.",num);
return 0;
}```

输出1：

```Enter an integer you want to check: 25
25 is odd.```

输出2：

```Enter an integer you want to check: 12
12 is even.```

也可以用条件运算符解决：

```/* C program to check whether an integer is odd or even using conditional operator */

#include <stdio.h>
int main(){
int num;
printf("Enter an integer you want to check: ");
scanf("%d",&num);
((num%2)==0) ? printf("%d is even.",num) : printf("%d is odd.",num);
return 0;
}```

## 11、C语言检查是元音还是辅音

源代码：

```#include <stdio.h>
int main(){
char c;
printf("Enter an alphabet: ");
scanf("%c",&c);
if(c=='a'||c=='A'||c=='e'||c=='E'||c=='i'||c=='I'||c=='o'||c=='O'||c=='u'||c=='U')
printf("%c is a vowel.",c);
else
printf("%c is a consonant.",c);
return 0;
}```

输出1：

```Enter an alphabet: i
i is a vowel.```

输出2：

```Enter an alphabet: G
G is a consonant.```

也可以用条件运算符解决

```/* C program to check whether a character is vowel or consonant using conditional operator */

#include <stdio.h>
int main(){
char c;
printf("Enter an alphabet: ");
scanf("%c",&c);
(c=='a'||c=='A'||c=='e'||c=='E'||c=='i'||c=='I'||c=='o'||c=='O'||c=='u'||c=='U') ? printf("%c is a vowel.",c) : printf("%c is a consonant.",c);
return 0;
}```

输出结果和上面的程序相同。

## 12、C语言实现从三个数值中查找最大值

实现1：

```/* C program to find largest number using if statement only */

#include <stdio.h>
int main(){
float a, b, c;
printf("Enter three numbers: ");
scanf("%f %f %f", &a, &b, &c);
if(a>=b && a>=c)
printf("Largest number = %.2f", a);
if(b>=a && b>=c)
printf("Largest number = %.2f", b);
if(c>=a && c>=b)
printf("Largest number = %.2f", c);
return 0;
}```

实现2：

```/* C program to find largest number using if...else statement */

#include <stdio.h>
int main(){
float a, b, c;
printf("Enter three numbers: ");
scanf("%f %f %f", &a, &b, &c);
if (a>=b)
{
if(a>=c)
printf("Largest number = %.2f",a);
else
printf("Largest number = %.2f",c);
}
else
{
if(b>=c)
printf("Largest number = %.2f",b);
else
printf("Largest number = %.2f",c);
}
return 0;
}```

实现3：

```/* C Program to find largest number using nested if...else statement */

#include <stdio.h>
int main(){
float a, b, c;
printf("Enter three numbers: ");
scanf("%f %f %f", &a, &b, &c);
if(a>=b && a>=c)
printf("Largest number = %.2f", a);
else if(b>=a && b>=c)
printf("Largest number = %.2f", b);
else
printf("Largest number = %.2f", c);
return 0;
}```

输出结果相同：

```Enter three numbers: 12.2
13.452
10.193
Largest number = 13.45```

## 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。

英文原文：C Programming Examples via:codeceo