P177. Implement user defined ( atof ) function.

 

#include<stdio.h>

#include<stdlib.h>

double my_atof(const char *);

void main(int argc,char **argv)

{

        int flag,i;

        if(argc<2)

                printf("Usage: a.out String \n");

 

        double num = my_atof(argv[1]);

        printf("%f\n",num);

}

 

double my_atof(const char *p)

{

    int i;

    float c,num,num1;

 

    if(p[0]=='-' || p[0]=='+')

        i=1;

    else

        i=0;

 

    for(num=0;p[i];i++)

    {

        if(p[i]>'0' && p[i]<'9')

        {

            num=num*10+(p[i]-48);

        }

        else if(p[i]=='.')

            break;

        else

                goto L1;

    }

    i++;

    for(num1=0,c=1;p[i];i++)

    {

        if(p[i]>'0' && p[i]<'9')

        {

            num1=num1*10+(p[i]-48);

            c=c*10;

        }

        else

                break;

    }

 

 

    num1=num1/c;

    num=num + num1;

 

 

    if(p[0]=='-')

        num=-num;

    L1:

    return num;

 

}