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C Primer Plus 练习本

简介

用来存自己的练习答案，看情况存，简单的写完就过了

5.11

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#include <stdio.h>
#define SCALE 60
void main(void)
{
    int tmins = 1, mins,hours;
    while(tmins > 0)
        {
            printf("How many minutes?\n");
            scanf("%d", &tmins);
            mins = tmins % SCALE;
            hours = tmins / SCALE;
            if(tmins>0)
            {
                printf("%d minutes = %d hours,%d minutes\n",tmins,hours,mins);
            }
            else
            {
                printf("Bye");
            }
            
        }
}

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#include <stdio.h>
void main(void)
{
    int init;
    printf("What's the int number?\n");
    scanf("%d",&init);
    int target = init +11;
    while (++init < target ) // ++init < init + 11 会无限判断为True 因为右边也在变..
    {
        printf("%d\t", init);
    }
}

7

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#include <stdio.h>
void cube(double val);

int main(void)
{
    double init;
    printf("Input a double num:");
    scanf("%lf",&init); //double对应转换说明%lf
    cube(init);
    return 0;
}

void cube(double val)
{
    printf("%f",val*val*val);
}

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#include <stdio.h>
void Temperatures(double val);

int main(void)
{
    double init;
    printf("Input a Fahrenheit degree(q to quit):\n");
    while (scanf("%lf",&init) == 1) // 不要在这里加分号...不然while循环体就是空的了(踩坑)
    {
        Temperatures(init);
    }
    printf("Bye");
    return 0;

}

void Temperatures(double val)
{
    double c = 5.0*(val-32)/9;
    double k = c+273.16;
    printf("%f °F = %f °C = %f K \n",val,c,k);
}

6.16

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#include<stdio.h>
int main(void)
{
    char alphabet[26];
    int i;
    for(i=0;i<26;i++)
    {
        alphabet[i] = 'a' + i;
    }
    for(i=0;i<26;i++)
    {
        printf("%c",alphabet[i]);
    }
}

2

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#include <stdio.h>
int main(void)
{
    int i, n;
    for (i = 0; i < 6; i++)
    {
        for (n = 0; n <= i; n++)
        {
            printf("%c", '$');
        }
        printf("\n");
    }
}

3

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#include <stdio.h>
int main(void)
{
    char last;
    char start;
    for (last = 'F'; last >= 'A';last--)
    {
        for (start = 'F'; start >= last;start-- )
        {
            printf("%c",start);
        }
        printf("\n");
    }
}

4

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#include <stdio.h>
int main(void)
{
    int line;
    char letter = 'A';
    int count;
    for (line = 0; line < 6; line++)
    {
        for (count = 0; count <= line; count++,letter++)
        {
            printf("%c",letter);
        }
        printf("\n");
    } 
}

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#include <stdio.h>
int main(void)
{
    int start,end;
    
    printf("A start and a end num splited by comma:\n");
    scanf("%d,%d",&start,&end);
    printf("Num\tSuqare\tCube\n");
    for (int i = start; i <= end; i++)
    {
        printf("%d\t%d\t%d\n",i,i*i,i*i*i);
    }
}

7

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#include <stdio.h>
#include <string.h>
int main(void)
{
    char word[20];
    int len;
    printf("Input a word:\n");
    scanf("%s",&word);
    len = strlen(word)-1; // 最后一个\0不考虑
    
    for (;len >= 0; len--) //不要在这里直接操作size_t类型
    {
        printf("%c",word[len]);
    }
}

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#include <stdio.h>
#include <string.h>
int main(void)
{
    double num1,num2;
    printf("Two float nums splited by spacing(q to quit):\n");
    while( scanf("%lf %lf",&num1,&num2) == 2) //scanf成功读取后返回值不是布尔值，是成功读取的参数数量..
    {
        printf("%lf\n", (num1-num2) / num1*num2);
        printf("Two float nums splited by spacing(q to quit):\n");
    }
}

11

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#include <stdio.h>
#include <string.h>
int main(void)
{
    int nums[8];
    for ( int i = 0; i <=7; i++)
    {
        printf("Now is no.%d\n",i);
        scanf("%d",&nums[i]);
    }
    printf("Done.\n");
    int len = sizeof(nums)/sizeof(nums[0]) -1 ;// sizeof返回值是bytes,除以单位元素大小就是数组长度。因为索引从0开始所以这里-1
    for (; len >= 0; len--)
    {
        printf("%d\n",nums[len]);
    }   
}

12

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#include <stdio.h>
int main(void)
{
    int i; // 数列大小
    printf("How many times?\n");
    while (scanf("%d", &i) == 1)
    {
        int denominator = 1; // 循环中变化的分母
        double expression = 0; // 全是正数的级数
        double expression2 =0; // 交错级数
        int num = 1; // 用于判定正负号
        for (; denominator <= i; denominator++, num *= (-1))
        {
            expression = expression + (double)1 / denominator;
            expression2 = expression2 + (double)1 / denominator * num;
            printf("%lf %lf\n", expression,expression2);
        }
        printf("Done.\n");
        printf("How many times?\n");
    }
}

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#include <stdio.h>
#include <math.h>
int main(void)
{
    int i;
    int array[8];
    int len = sizeof(array)/sizeof(array[0]);
    for (i = 0; i <= len - 1; i++)
    {
        array[i] = pow(2,i);
    }
    i = 0;
    do
    {
        printf("%d\n",array[i]);
        i++;
    } 
    while (i <= len-1);
}

14

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#include <stdio.h>
int main(void)
{
    double nums[8];
    double sums[8];

    int i, j;
    int len = sizeof(nums) / sizeof(nums[0]);
    printf("Now input nums by order:\n");
    for (i = 0; i < len - 1; i++)
    {
        scanf("%lf", &nums[i]);
    }
    for (j = 0; j < len - 1; j++)
    {
        double sumtemp;
        for (i = 0; i <= j; i++)
        {
            sumtemp += nums[i];
        }
        sums[j] = sumtemp;
    }
    for (i = 0; i < len - 1; i++)
    {
        printf("%lf\t", nums[i]);
    }
    printf("\n");
    for (i = 0; i < len - 1; i++)
    {
        printf("%lf\t", sums[i]);
    }
}
/*
1.000000        2.000000        3.000000        4.000000        5.000000        6.000000        7.000000
1.000000        4.000000        10.000000       20.000000       35.000000       56.000000       84.000000
*/

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#include <stdio.h>

int main(void)
{
    int i;
    char input[255];
    for ( i = 0; i <= 255 && input[i] != '\n'; i++)
    {
        scanf("%c", &input[i]);
        if (input[i] == '\n')
        {
            break;
        }
    }
    for (;i >= 0; i--)
    {
        printf("%c",input[i]);
    }
    
    return 0;
}

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#include <stdio.h>
int main(void)
{
    int year = 0;
    double dap = 100, dei = 100;
    double r_dei = 1.05;
    while (dei <= dap)
    {
            dap += 110.0;
            dei *= r_dei;
            year++;
    }
    printf("%d",year);
    // for (year = 0; dei <= dap; ++year)
    // {
    //     dap += 110.0;
    //     dei *= r_dei;
    // }
    // printf("%d",year);
}

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#include <stdio.h>
int main(void)
{
    int year = 0;
    double balance = 1e5;
    while (balance > 0)
    {
        balance *= 1.08;
        balance -= 1e4;
        year++;
    }
    printf("%d",year);
}

18

do-while

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#include <stdio.h>
int main(void)
{
    int friends = 5;
    int week = 1;
    do
    {
        friends -= week;
        friends *= 2;
        printf("Week%d Frienders:%d\n",week,friends);
        week++;
    } while (friends <= 150);
}

while

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#include <stdio.h>
int main(void)
{
    int friends = 5;
    int week = 0;
    while (friends <= 150)
    {
        week++;
        friends -= week;
        friends *= 2;
        printf("Week%d Frienders:%d\n", week, friends);
    }
}

for

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#include <stdio.h>
int main(void)
{
    int friends;
    int week;
    for (friends = 5, week = 1; friends <= 150; week++)
    {
        friends -= week;
        friends *= 2;
        printf("Week%d Frienders:%d\n", week, friends);
    }
}

7.12

5

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#include <stdio.h>
int main(void)
{
    char ch;
    int count = 0;

    while( scanf("%c",&ch) && ch != '#' )
    {
        switch (ch)
        {
        case '.': 
            ch = '!';
            count++;
            break;
        case '!':
            ch = '!!';
            count++;
        default:
            break;
        }
    }
    printf("%d",count);
}

6

非提示解法

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#include <stdio.h>
int main(void)
{
    int num = 0;
    int count = 0;
    char ch;
    while (scanf("%c", &ch) && ch != '\n')
    {
        if (ch == 'e')
        {
            num = 1;
        }
        else if (ch == 'i')
        {
            if (num == 1)
            {
                count++;
                num = 0;
            }
            else
            {
                continue;
            }
        }
    }
    printf("%d", count);
}

9.11

3

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void printline(char ch, int line, int num)
{
    for (; line > 0; line--)
    {
        for (int count =num ; count > 0; count--) //每行循环重新初始化count为num
        {
            putchar(ch);
        }
        putchar('\n');
    }
}

4

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double harmonic(double x,double y)
{
    return 2/(1/x+1/y);
}

5

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double large_of(double *x,double *y)
{
    double large = (*x<*y)? *y:*x;
    *x = large;
    *y = large;  //不用if了，反正就俩值，直接赋
}

6

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double sort(double *x,double *y, double *z)
{
    double i;
    if (*x<*y)
    {
        i = *y;
        *y = *x;
        *x = i;
    }
    if (*x<*z)
    {
        i = *z;
        *z = *x;
        *x = i;
    }
    if (*y<*z)
    {
        i = *z;
        *z = *y;
        *y = i;
    }
}

7

这道题题目有点绕

利用ctype.h简化了代码，并未对checkChar返回的-1做任何处理

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#include <stdio.h>
#include <ctype.h>
void checkStdInput();
int checkChar(char ch);

int main(void)
{
    checkStdInput();
    return 0;
}

void checkStdInput()
{
    char ch;
    while ((ch = getchar()) != EOF)
    {
        checkChar(ch);
    }
}

int checkChar(char ch)
{
    if (isalpha(ch))
    {
        int index = (islower) ? ch - 'a' + 1 : ch - 'A' + 1;
        printf("%c is a letter and the index is %d\n", ch, index);
    }  
    else
    {
        return -1;
    }
}

8

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double power(double num, int n)
{
    double res = num;
    if (n == 0)
    {
        return 1;
    }
    else if (n == 1)
    {
        return num;
    }

    else
    {
        if (n > 0)
        {
            for (; n > 1; n--)
            {
                res *= num;
            }
        }
        else
        {
            n = -n;
            for (; n > 1; n--)
            {
                res *= num;
            }
        }
        return 1 / res;
    }
}

10

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void to_base_n(int x, int base) 
{
    int r;
    r = x % base;
    if (x >= base)
        to_base_n(x / base, base);

    putchar('0' + r);
    return;
}

11

未加任何限定，无限打印

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void Fibonacci()
{
    int a = 0, b = 1;
    printf("%d %d", a, b);
    int num = a + b;
    printf(" %d",num);
    while (1)
    {
        a = b;
        b = num;
        num = a + b;
        printf(" %d",num);
    }
}

打印指定前 n 项

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void Fibonacci(int n)
{
    n = n-3; // 前三项不在循环里
    int a = 0, b = 1,c=1;   
    printf("%d %d %d",a,b,c);
    for (; n > 0; n--)
    {
        a = b;
        b = c;
        c = a + b;
        printf(" %d", c);
    }
}

10.13

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#include <stdio.h>
#define MONTHS 12 // number of months in a year
#define YEARS 5   // number of years of data
int main(void)
{
    // initializing rainfall data for 2010 - 2014
    const float rain[YEARS][MONTHS] =
        {
            {4.3, 4.3, 4.3, 3.0, 2.0, 1.2, 0.2, 0.2, 0.4, 2.4, 3.5, 6.6},
            {8.5, 8.2, 1.2, 1.6, 2.4, 0.0, 5.2, 0.9, 0.3, 0.9, 1.4, 7.3},
            {9.1, 8.5, 6.7, 4.3, 2.1, 0.8, 0.2, 0.2, 1.1, 2.3, 6.1, 8.4},
            {7.2, 9.9, 8.4, 3.3, 1.2, 0.8, 0.4, 0.0, 0.6, 1.7, 4.3, 6.2},
            {7.6, 5.6, 3.8, 2.8, 3.8, 0.2, 0.0, 0.0, 0.0, 1.3, 2.6, 5.2}};
    int year, month;
    float subtot, total;
    float *p = rain;
    float(*p1)[12] = rain;

    printf(" YEAR    RAINFALL  (inches)\n");
    for (year = 0, total = 0; year < YEARS; year++)
    { // for each year, sum rainfall for each month
        for (month = 0, subtot = 0; month < MONTHS; month++)
            subtot += *p++;
        //or this: subtot += *(*(rain + year) + month);
        printf("%5d %15.1f\n", 2010 + year, subtot);
        total += subtot; // total for all years
    }
    printf("\nThe yearly average is %.1f inches.\n\n",
           total / YEARS);
    printf("MONTHLY AVERAGES:\n\n");
    printf(" Jan  Feb  Mar  Apr  May  Jun  Jul  Aug  Sep  Oct ");
    printf(" Nov  Dec\n");

    for (month = 0; month < MONTHS; month++)
    { // for each month, sum rainfall over years
        for (year = 0, subtot = 0; year < YEARS; year++)
            subtot += *(*(rain + year) + month);
        //or use p1: subtot += *(*(p1+year)+month) ;
        printf("%4.1f ", subtot / YEARS);
    }
    printf("\n");

    return 0;
}

2

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void copy_arr(double target[], double source[], int len)
{
    for (int count = 0; count <= len-1 ; count++)
    {
        target[count] = source[count];
    }
    
}
void copy_ptr(double *target, double *source, int len)
{
    for (int count = 0; count <= len-1;count++)
    {
        *(target++) = *(source++);
    }
    
}
void copy_ptrs(double *target, double *start, double *end)
{
    for (; start <= end-1;)
    {
        *(target++) = *(start++);
    }   
}

3

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#include <stdio.h>
int array_max(int array[], int len);
int max(int a, int b);

int main(void)
{
    int array[5] = {5, 7, 1232, 8, 1};
    int *p = (int[6]){2323, 2,1243,34547,45,3};//复合字面量，或者说匿名数组？
    int res = array_max(array, 5);
    int res2 = array_max(array, 6);
    printf("%d %d", res,res2);
}

int array_max(int array[], int len) // 数组名和数组长度
{
    int a = array[0], b;

    for (int i = 1; i <= len - 1; i++)
    {

        b = array[i];
        if (max(a, b) == b)
        {
            a = b;
            continue;
        }
        else
        {
            continue;
        }
    }
    return a;
}

int max(int a, int b) // 手写一个max()
{
	return (a>=b)?a:b;
}
/*
1232 34547
*/

4

上一道题简单改了改

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#include <stdio.h>
int array_max_index(double array[], int len);
double max(double a, double b);

int main(void)
{
    // 懒得写小数点，下面包含隐式类型转换
    double array[5] = {5, 7123, 1232, 8, 1};
    double *p = (double[6]){2323, 2, 1243, 34547, 45, 3}; //复合字面量,
    int res1 = array_max_index(array, 5);
    int res2 = array_max_index(p, 6);
    printf("%d %d", res1, res2);
}

int array_max_index(double array[], int len) // 数组名和数组长度
{
    double a = array[0], b;
    int maxindex = 0;
    for (int i = 1; i <= len - 1; i++)
    {
        b = array[i];
        if (max(a, b) == b)
        {
            a = b;
            maxindex = i;
            continue;
        }
        else
        {
            continue;
        }
    }
    return maxindex;
}

double max(double a, double b)
{
    return (a>=b)?a:b;
}
// 1 3

5

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#include <stdio.h>
double array_max_min(double array[], int len);


int main(void)
{
    double arr[5] = {1, 2, 3, 4, 6};
    double res = array_max_min(arr, 5);
    printf("%lf", res);
}
double array_max_min(double array[], int len)
{
    double max = array[0];
    double min = array[0];
    for (int i = 1; i < len; i++)
    {
        if (max < array[i])
            max = array[i];
        else if (min > array[i])
            min = array[i];
    }
    return max - min;
}

// 5.000000

6

双指针解决

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void array_reverse(double arr[], int len)
{
    if (len % 2 == 0) // 偶数长度
    {
        double temp;
        double *start = arr;
        double *end = &arr[len - 1];
        for (int i = 0; i < len / 2; i++)
        {
            temp = *start;
            *start = *end;
            *end = temp;

            start++;
            end--;
        }
    }
    else
    {
        double temp;
        double *start = arr;
        double *end = &arr[len - 1];
        for (int i = 0; i < (len / 2) + 1; i++)
        {
            temp = *start;
            *start = *end;
            *end = temp;

            start++;
            end--;
        }
    }
}

7

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void copy_2darray(int row, int column, double array[][column], double newarray[][column])
// 复制一个二维数组的内容到另一个二维数组
//参数: 行，列，原数组，新数组
{
    double (*ptr)[column] = array;
    double (*ptr_new)[column] = newarray;
    for (int i = 0; i < row; i++) //二维
    {
        ptr = array + i;
        ptr_new = newarray + i;
        for (int j = 0; j < column; j++) //一维
        {
            *(*ptr_new+j) = *(*ptr+j); // newarray[i][j] = array[i][j]
        }
    }
}

利用”内层越界”的方式，可以直接当一维数组处理

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void copy_2darray(int row, int column, double array[][column], double newarray[][column])
{
    for (int i = 0; i < row*column; i++)
    {
        newarray[0][i] =array[0][i];
    }
}

9

复制函数参考第 7 题

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void show_2darray(int row, int column, double array[][column])
{
    for (int i = 0; i < row * column ; i++)
    {
        if ((i + 1) % column == 0)
        {
            printf("%g\n", array[0][i]);
        }
        else
        {
            printf("%g\t", array[0][i]);
        }
    }
}

10

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void array_sumup(int len,int a[], int b[],int sum[])
{
    for (int i = 0; i < len; i++)
    {
        sum[i] = a[i]+b[i];
    }
}

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#include <stdio.h>
void data2array(double array[3][5]);
void show_average_subarray(double array[3][5]);
double average_subarray(double subarray[5]);
double average_all(double array[3][5]);
double maximum(double array[3][5]);
int main(void)
{
    double array[3][5];
    printf("Input 3 lines of double numbers(splited by space, enter to the next row):\n");
    data2array(array);
    show_average_subarray(array);
    double avr_all = average_all(array);
    double max = maximum(array);
    printf("The average of all is: %lf\n", avr_all);
    printf("The maximum is: %lf", max);
}

void data2array(double array[3][5])
{
    for (int i = 0; i < 3; i++)
    {
        double(*start)[5] = array + i;
        fflush(stdin);
        scanf("%lf %lf %lf %lf %lf", *start, (*start) + 1, (*start) + 2, (*start) + 3, (*start) + 4);
    }
}
void show_average_subarray(double array[3][5])
{
    double sum;
    printf("Average of each subarray:\n");
    for (int i = 0; i < 3; i++)
    {
        double(*subarray)[5] = array + i;
        double avr_subarray = average_subarray(subarray);
        printf("Subarray%d: %g\n", i, avr_subarray);
    }
}
double average_subarray(double subarray[5])
{
    double subsum;
    for (int i = 0; i < 5; i++)
    {
        subsum += subarray[i];
    }
    return subsum / 5;
}
double average_all(double array[3][5])
{
    double sum;
    for (int i = 0; i < 15; i++)
    {
        sum += array[0][i];
    }
    return sum / 15;
}
double maximum(double array[3][5])
{
    double max = array[0][0];
    for (int i = 1; i < 15; i++)
    {
        max = (array[0][i] > max) ? array[0][i] : max;
    }
    return max;
}

11.13

1

危险

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void getn(int n, char array[])
{
	while (n-->0)
	{
		*array++ = getchar();
	}
}

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危险

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void getn(int n, char array[])
{
	fflush(stdin);
	char tmp;
	for (;n>0;n--)
	{
		tmp = getchar();
		if(tmp != ' '&& tmp != '\n' && tmp!='\t')
		{
			*array++ = tmp;
		}
		else
		{
			break;
		}
	}
}

3

危险

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void word(char array[])
{
	fflush(stdin);
	scanf("%s",array);
}

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char* _strchr(char *string, char ch)
{
	while (*string)
	{
		if ( *string == ch)
		{
			char *ptr = &ch;
			return ptr;
		}
		else
		{
			string++;
		}
	}
	return NUll;
}

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char *mystrncpy(char *s1, char *s2, int n)
{
	char *s1end = s1 + strlen(s1);
	if (strlen(s2) >= n)
	{
		while (n--)
		{
			*s1end++ = *s2++;
		}
	}
	else
	{
		int s2len = strlen(s2);
		while (s2len--)
		{
			*s1end++ = *s2++;
		}
		n = n - s2len;
		while (n--)
		{
			*s1end++ = ' ';
		}
	}
	return s1;
}

C Primer Plus 练习本

https://bakaft.github.io/2020/07/16/C-Primer-Plus-练习本/

Author

BakaFT

Posted on

2020-07-16

Updated on

2023-12-28

Licensed under

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