C类型转换函数

1.字符串→整型

int atoi(char s[]){    int i,n,sign;    for(i=0;isspace(s[i]);i++)//skip front spaces        ;    sign=(s[i]=='-')? -1:1;    if(s[i]=='+'||s[i]=='-')  //skip the sign        i++;    for(n=0;isdigit(s[i]);i++)        n=n*10+(s[i]-'0');    return sign*n;}

2.整型→字符串

void itoa(int n,char s[]){    int i,sign;    if((sign=n)<0)        n=-n;    i=0;    do{        s[i++]=n%10+'0';    }while((n/=10)>0);    if(sign<0)        s[i++]='-';    s[i]='\0';    reverse(s);}void reverse(char s[]){    int c,i,j;    for(i=0,j=strlen(s)-1;i<j;i++,j--){        c=s[i];        s[i]=s[j];        s[j]=c;    }}

3.字符串→浮点

//atof:translate string into double floatdouble atof(char s[]){    double val,power;    int i,sign;    for(i=0;isspace(s[i]);i++)//skip space        ;    sign=(s[i]=='-')?-1:1;    if(s[i]=='+'||s[i]=='-')        i++;    for(val=0.0;isdigit(s[i]);i++)        val=val*10.0+(s[i]-'0');    if(s[i]=='.')        i++;    for(power=1.0;isdigit(s[i]);i++){        val=10.0*val+(s[i]-'0');        power*=10.0;    }    return sign*val/power;}