C程序设计语言学习--控制流（折半、atoi、itoa）

1：折半查找

int binsearch(int x,int v[],int n)
{
    int low,high,mid;
    
    low = 0;
    high = n -1;
    mid = (low + high)/2;

    while(low <= high && x != v[mid]){
        if(x > v[mid]){
            low = mid +1;
        }else{
            high = mid -1;
        }
        mid = (lov + high)/2;
    }

    if(x == v[mid]){
        return mid;
    }else
        return -1;
}

2:编写atoi()函数

int myatoi(char s[])
{
    int i,sig = 1,n;

    for(i = 0;isspace(s[i]);i ++)
        ;

    sig = (s[i] == '-') ? -1 :1;

    if(s[i] == '+' || s[i] == '-')
        i ++;

    for(n = 0;isdigit(s[i]);i ++){
        n = n * 10 + (s[i] - '0') ;
    }

    return sig * n;
}

3：编写itoa()功能函数（另一种方法：用栈）

#include

#define MAXLEN 32

void itoa(int num,char s[]);    
void reverse(char s[]);        //翻转字符串

int main(void)
{
    int i = 98762;
    char s[MAXLEN];

    itoa(i,s);
    printf("%s",s);
    
    return 0;
}


void itoa(int num,char s[])
{
    int i,sig;

    if(num < 0)    
        sig = num;
    i = 0;
    do{    
        s[i++] = abs(num % 10) + '0';
    }while((num = num / 10) != 0);


    if(sig < 0)
        s[i++] = '-';
    s[i] = '\0';

    reverse(s);
}

/*
    将逆序的字符串进行翻转
*/
void reverse(char s[])
{
    int i = 0;
    while(s[i] != '\0'){
        i ++;
    }
    i --;

    int low = 0;
    char tmp;
    while(low <= i){
        tmp = s[low];
        s[low] = s[i];
        s[i] = tmp;
        low ++; i --;
    }
}