C和指针第三章--编程练习

1.正数的平方根

#include <stdio.h>

int main(void)
{
    float Number, CurAppro, PreAppro;

    printf("please input a number:\n");
    scanf("%f", &Number);
    if(Number < 0)
    {
        printf("number must is positive\n");
        return 0;
    }

    CurAppro = 1;
    PreAppro = 0;
    while(CurAppro != PreAppro)
    {
        PreAppro = CurAppro;
        CurAppro = (CurAppro + Number / CurAppro) / 2;
        printf("%f\n", CurAppro);
    }

    printf("%f\n", CurAppro);

    return 0;
}

2.打印1-100的质数

#include <stdio.h>

int main(void)
{
    int Number, divisor;

    printf("1\n2\n"); 

    for(Number = 3; Number <= 100; Number += 2)
    {
        for(divisor = 3; divisor < Number; divisor += 2)
        {
            if(Number % divisor == 0)
                break;
        }

        if(divisor >= Number)
            printf("%d\n", Number);
    }

    return 0;
}

这里的循环控制变量每次加二，表示只计算奇数，减少了一半的计算量。

3.用户输入三角形3条边的长度，判断这个三角形是什么三角形

#include <stdio.h>

int main(void)
{
    int a, b, c;

    printf("please enter the length of three edges\n");
    while(1)
    {
        while(scanf("%d %d %d", &a, &b, &c) != 3)
        {
            while(getchar() != '\n');
            printf("enter again\n");
        }
        while(getchar() != '\n');

        /*
        **假设c是最短边，b是次短边，a是最长边 
        */
        if(a < b)
        {
            int tmp = b;
            b = a;
            a = tmp;
        }
        if(a < c)
        {
            int tmp = c;
            c = a;
            a = tmp;
        }
        if(b < c)
        {
            int tmp = b;
            b = c;
            c = tmp;
        }

        if((c > 0) && (a - b < c))
        {
            if(a == b && b == c)
            {
                printf("Equilateral triangle\n");
            }
            else if(b == c || a == b)
            {
                printf("Dengyao triangle\n");
            }
            else
            {
                printf("Not equilateral triangle\n");
            }
        }
        else
            printf("not a triangle\n");
    }

    return 0;
}

4.编写函数copy_n(char dst[], char src[], int n);

void copy_n(char dst[], char src[], int n)
{
    int DstPos, SrcPos;

    SrcPos = 0;

    for(DstPos = 0; DstPos < n; DstPos++)
    {
        dst[DstPos] == src[SrcPos];
        if(src[SrcPos] != '\0')
        {
            SrcPos++;
        }
    } 
}

5.从标准输入一行一行读取文本，如果文件中有两行或更多行相邻的文本内容，就打印其中的一行，其余的不打印。可以假设问本行的长度不会超过128字节。

int main(void)
{
    int HavePrint = 0;
    char CurLine[128];
    char PreLine[128];

    if(gets(PreLine) != NULL)
    {
        while(gets(CurLine) != NULL)
        {
            if(strcmp(PreLine, CurLine) != 0)   
            {
                HavePrint = 0;
                strcpy(PreLine, CurLine); 
            }
            else if(HavePrint == 0)
            {
                HavePrint = 1;
                printf("%s\n", CurLine);
            }

        }   
    }   
    return 0;
}

6.编写一个函数,原型如下：
int substr(char dst[], char stc[], int start, int len);
是从src数组起始位置开始偏移start个字符的位置，最多复制len个非NUL字符到dst数组。复制完成后dst必须以NUL字节结尾。

int substr(char dst[], char src[], int start, int len)
{
    int startPos;
    int dstPos;

    if(start < 0 || len < 0)
    {
        return -1;
    }

    for(startPos = 0; startPos < start && src[startPos] != '\0'; startPos++)
        ;

    for(dstPos = 0; dstPos < len; dstPos++)
    {
        dst[dstPos] = src[startPos];
        if(src[startPos] != '\0')
        {
            startPos++;
        }
    }
    dst[dstPos] = '\0';

    return 0;
} 

7.去除字符串中的多余空格：
void deblank( char string[] );
当字符串中有一个地方由一个或多个连续的空格组成，就改为单个空格、

int IsWhite(char c)
{
    return (c == ' ') || (c == '\t') || (c == '\n') || (c == '\v'); 
}

void deblank(char string[])
{
    char *destPos, *SrcPos;
    char c;
    int IsFirstWhite;

    IsFirstWhite = 1;
    for(SrcPos = string, destPos = string; (c = *SrcPos) != '\0'; SrcPos++)
    {
        if(IsWhite(c))
        {
            if(IsFirstWhite == 1)
            {
                *destPos++ = ' ';
                IsFirstWhite = 0;
            }
        }
        else
        {
            *destPos++ = *SrcPos;
            IsFirstWhite = 1;
        }
    } 
    *destPos = '\0';
}

跟合并内容相同的行那题有些相似