w3resource

C atoi() function

C atoi() function - Convert a string to an integer

The atoi() function is used to convert a character string to an integer value.

Syntax:

int atoi(const char *str)

Parameters:

Name Description Required /Optional
str String to be converted. Required

Return value from atoi()

  • Returns an integer value that is produced by interpreting the input characters as a number.
  • If the function cannot convert the input to a value of that type return value is 0.
  • The return value is undefined in the case of an overflow.

Example: atoi() function

The following example shows the usage of atoi() function.


#include <stdlib.h>
#include <stdio.h>
 
int main(void)
{
    int in_val;
    char *s;
    s = " -4938";
    printf("String value: %s",s);
    in_val= atoi(s); 
    printf("\nInteger value = %d\n",in_val);
    s = "+4938";
    printf("\nString value: %s",s);
    in_val= atoi(s); 
    printf("\nInteger value = %d\n",in_val);
    s = "4938";
    printf("\nString value: %s",s);
    in_val= atoi(s); 
    printf("\nInteger value = %d\n",in_val);
    s = "0038";
    printf("\nString value: %s",s);
    in_val= atoi(s); 
    printf("\nInteger value = %d\n",in_val);
    s = "003800";
    printf("\nString value: %s",s);
    in_val= atoi(s); 
    printf("\nInteger value = %d\n",in_val);
}

Output:

String value:  -4938
Integer value = -4938

String value: +4938
Integer value = 4938

String value: 4938
Integer value = 4938

String value: 0038
Integer value = 38

String value: 003800
Integer value = 3800

C Programming Code Editor:

Previous C Programming: C atof()
Next C Programming: C atol()



Follow us on Facebook and Twitter for latest update.

C Programming: Tips of the Day

What's the point of const pointers?

const is a tool which you should use in pursuit of a very important C++ concept:

Find bugs at compile-time, rather than run-time, by getting the compiler to enforce what you mean.

Even though it does not change the functionality, adding const generates a compiler error when you're doing things you didn't mean to do. Imagine the following typo:

void foo(int* ptr)
{
    ptr = 0;// oops, I meant *ptr = 0
}

If you use int* const, this would generate a compiler error because you're changing the value to ptr. Adding restrictions via syntax is a good thing in general. Just don't take it too far -- the example you gave is a case where most people don't bother using const.

Ref : https://bit.ly/33Cdn3Q