C atof()

The atof() function is defined in the stdlib.h header file. It helps to convert a given string argument(str) into a floating-point value ie type double.

double atof(const char *str); #where str should be a string


atof() Parameters: 

The atof() function takes a single parameter. In C language typecasting is supported by stdlib.h headerfile.

Parameter Description Required / Optional
str  the string having the representation of a floating-point number Required

atof() Return Value

The return value of atof() function is a floating-point number as a double value.

Input Return Value
successful double value
invalid conversion zero

Examples of atof()

Example 1: Working of atof() function in C?

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
   float f;
   char st[20];
   strcpy(st, "23333333");
   f = atof(st);
   printf("String is %s, Float value = %f\n", st, f);

   strcpy(st, "Hi how are you");
   f = atof(st);
   printf("String is %s, Float value = %f\n", st, f);



String is 23333333, Float value = 23333333.000000
String is Hi how are you, Float value = 0.000000

Example 2: How atof() works in C?

#include <stdio.h>

int main (){
  char x[10] = "3.14";
    float pi = atof(x);
    printf("pi value is %f\n", pi);
    return 0;


pi value is 3.140000