make the user defined atof() implementation more 'correct' ?

Can the library definition of atof() be found somewhere ?

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

float str_to_float(char *);
void float_to_str(float,char *);

int main(){
    int max_size;
    float x;
    char *arr;
    printf("Enter max size of string : ");
    scanf("%d",&max_size);
    arr=malloc((max_size+1)*sizeof(char));
    scanf("%s",arr);
    x=str_to_float(arr);
    printf("%f\n%f",x,atof(arr));
    return 0;
}

float str_to_float(char *arr){
    int i,j,flag;
    float val;
    char c;
    i=0;
    j=0;
    val=0;
    flag=0;
    while ((c = *(arr+i))!='\0'){
//      if ((c<'0')||(c>'9')) return 0;
        if (c!='.'){
            val =(val*10)+(c-'0');
            if (flag == 1){
                --j;
            }
        }
        if (c=='.'){ if (flag == 1) return 0; flag=1;}
        ++i;
    }
    val = val*pow(10,j);
    return val;
}
by

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About C

C language is one of the most popular general-purpose programming language developed by Dennis Ritchie at Bell laboratories for UNIX operating system. The initial release of C Language was in the year 1972. Most of the desktop operating systems are written in C Language.

Key features:

  • Structured Programming
  • Popular system programming language
  • UNIX, MySQL and Oracle are completely written in C.
  • Supports variety of platforms
  • Efficient and also handle low-level activities.
  • As fast as assembly language and hence used as system development language.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition if-else is used.

if(conditional-expression) {
   // code
} else {
   // code
}

You can also use if-else for nested Ifs and if-else-if ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to if-else-if ladder.

switch(conditional-expression) {    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
...    
    
default:     
 // code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  // code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while(condition) {  
 // code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {
  // code 
} while (condition);

Arrays

Array is a collection of similar data which is stored in continuous memory addresses. Array values can be fetched using index. Index starts from 0 to size-1.

Syntax

One dimentional Array:

data-type array-name[size];

Two dimensional array:

data-type array-name[size][size];

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity.

Two types of functions are present in C

  1. Library Functions:

Library functions are the in-built functions which are declared in header files like printf(),scanf(),puts(),gets() etc.,

  1. User defined functions:

User defined functions are the ones which are written by the programmer based on the requirement.

How to declare a Function

return_type function_name(parameters);

How to call a Function

function_name (parameters)

How to define a Function

return_type function_name(parameters) {  
  //code
}