C和指针第九章的四个小代码

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#include <stdio.h>#include <stdlib.h>#include <string.h>//作用是将那个数字按照一定格式输出9_14_15void dollars( char *dest,char const *src );int main(){    char a[100];    char b[300];    printf("请输入数字\n");    gets(a);    dollars( b, a);    puts(b);    //printf("Hello world!\n");    return 0;}void dollars( char *dest,char const *src ){    int length, i;    if( dest == NULL || src == NULL )    {        return;    }    *dest++ = '$';    length = strlen(src);    if( length >= 3 )    {        for(i = length-2; i>0; )        {            *dest++ = *src++;            if(--i > 0 && i % 3 ==0 )                *dest++ = ',';        }    }    else    {        *dest ++= '0';    }    *dest++ = '.';    *dest++ = length < 2 ? '0':*src++;    *dest++ = length < 1 ? '0':*src;    *dest ='\0';}

#include <stdio.h>#include <stdlib.h>#include <string.h>//单词以空白字符分开，并且计算the出现的数目9_14_11int main(){    char a[100];    char *word;    char const whitespace[] = " \n\r\f\t\v ";    printf("输入一大句英文!\n");    gets(a);    int count = 0;    for( word = strtok( a, whitespace ); word != NULL; word = strtok( NULL, whitespace) )    {        if( strcmp( word, "the" ) == 0 )            count+=1;    }    printf( "%d\n", count );    return 0;}

#include <stdio.h>#include <stdlib.h>#include <stddef.h>//类似strcpy的一个函数，但是返回的是指向目标字符串末尾的指针char *mystrcpy(char const *dest, char const *src);int main(){    char a[10]="ABC";    char b[7]="CDefg";    // char *first;    //char *last;    //first = strcpy(a, b);    //puts(a);    mystrcpy(a, b);    /*int j;    j = strlen (a);    int i;    for(i=0; i < j; i++)    {        printf("%c",a[i]);    }*/    puts(a);    return 0;}char * mystrcpy(char const *dest, char const *src){    char *m,*n;    m = dest;    n = src;    char *p;    while(( *m++ = *n++ )!='\0')    ;    p=(m-1);    return p;}

#include <stdio.h>#include <stdlib.h>#include <stddef.h>//计算字符串的长度，也可以接受由于strnxx函数导致的没有'\0'的字符串长度，实际上就是看一个数组里有'\0'就计算那个长，否则就是数组长度int mystrlen( char const *string, int size );int main(){    char a[7]="ABC";    char b[5]="CDEFG";    strncpy(a, b, 5);    int count;    count = mystrlen(a, 8);    printf("%d\n", count);    return 0;}int mystrlen( char const *string, int size ){    int length = 0;    for(length = 0; length < size; length++)    {        if(*string++ == '\0')            break;    }    return length;}

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