The C language implements prime numbers, least common multiples, maximum common approx., number of input, prime number, number of completion, and daffodils algorithm.

1. Algorithms for prime numbers:

Two for loops are used. The outer loop is the required range. The inner loop ranges from 2 to SQRT (a value of + 1 in the outer loop range). A flag is set to indicate whether it is a prime number;

Specific implementation:

# Include <stdio. h>

# Include <math. h>

Int main (void)

{

Int I, J;

Bool flag = 0; // set a flag. 0 indicates a non-prime number, and 1 indicates a prime number;

For (I = 101; I <= 200; I ++) // calculate 101 ~ The prime number of 200, which is printed out;

{

For (j = 2; j <= SQRT (double) (I + 1); j ++)

{

If (I % J = 0)

{

Flag = 0;

Break;

}

Else

Flag = 1;

}

If (FLAG)

Printf ("% d", I );

}

Return 0;

}

2. Algorithms for daffodils:

It is mainly to know the concept of the number of daffodils, and then separate the single digit, ten digits and hundreds of digits;

The so-called "Daffodils" refers to a three-digit number, each digit of which is equal to the number itself.

Specific implementation:

# Include <stdio. h>

Int main (void)

{

Int I;

Int Weiwei, Shiwei, gewei;

For (I = 100; I <1000; I ++)

{

Int temp = 0;

Gewei = I % 10; // separate a bit;

Shiwei = I/10% 10; // separated by ten;

Wei = I/100; // separates hundreds of digits;

Temp = gewei * gewei + Shiwei * Shiwei + Wei * Wei;

If (I = temp)

Printf ("I = % d \ n", I );

}

Return 0;

}

3. algorithms for the maximum public approx. And the minimum public multiples:

The maximum common divisor must be the largest of the common divisor, that is, the last one in the common divisor;

The minimum public multiple must be the smallest of the Public multiples, that is, the first starting public multiple.

Specific implementation:

# Include <stdio. h>

Int main (void)

{

Int m, n, I, j;

Int GCD, LCM;

Printf ("Please input two integer \ n ");

Scanf ("% d", & M, & N );

For (I = 1; I <(M> n? M: N); I ++)

{

If (M % I = 0 & N % I = 0)

GCD = I; // obtain the last approximate number;

}

For (j = (M> n? M: N); j <= m * n; j ++)

{

If (J % m = 0 & J % N = 0)

{

LCM = J;

Break; // immediately jumps out of the loop when a public multiple is obtained;

}

}

Printf ("greatest common divisor is % d \ n", gcd );

Printf ("least common multiple is % d \ n", LCM );

Return 0;

}

4. Number of algorithms:

Definition: final number, that is, perfect number. If a number is equal to the sum of factors other than itself, this number is called final number.

Specific implementation:

# Include <stdio. h>

Int main (void)

{

Int I, j, R;

For (I = 1; I <= 1000; I ++)

{

R = 0;

For (j = 1; j <I; j ++)

{

If (I % J = 0) // This sentence is critical;

R = R + J;

}

If (r = I)

Printf ("perfect number is % d \ n", R );

}

Return 0;

}

5. The number of retrieval algorithms:

Definition: "Number of input" is a number. For example, if the number is 98789, the number is 98789, and the number is 98789. The number is the same as the number of reading.

Algorithm Implementation:

# Include <stdio. h>

# Include <string. h>

Int main (void)

{

Char STR [100];

Char * pA, * pb; // Use Pointer;

Printf ("Please input a string \ n ");

While (scanf ("% s", STR )! = EOF)

{

Pa = STR; // point to the first character;

PB = STR + strlen (STR)-1; // point to the last non-(\ 0) character;

While (* pA = * pb & Pa <Pb)

{

Pa ++;

Pb --;

}

If (Pa> = Pb) // indicates the number of input files;

Printf ("True \ n ");

Else

Printf ("false \ n ");

}

Return 0;

}

6. Prime Number algorithms:

Definition: prime number is a number that can only be divided by 1 and itself, such as 2, 3, 5, 7, 11 ......

Algorithm Implementation:

# Include <stdio. h>

Int main (void)

{

Int I, J;

Bool flag = true; // set the flag. The default value is true;

For (I = 2; I <= 100; I ++)

{

For (j = 2; j <I; j ++)

{

If (I % J! = 0)

{

Flag = true; // if it cannot be divisible, the flag is set to true;

}

Else

{

Flag = false; // if it can be divisible, set the flag to false and exit the loop;

Break;

}

}

If (flag = true) // when the flag is true, a number is printed;

Printf ("% d", I );

}

Return 0;

}