CS16 (UCSB CS Dept., P. Conrad)

notes on atoi()

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Here's a review of some of what we learned in lab03 about atoi()

atoi() can be used to convert strings such as "30" which are strings in C (i.e. char * values) into integer values like 30 that can be stored in an int variable.
As an example, we might write:
```
int x;
x = atoi("30");
```
One common use of atoi is access numbers typed on the command line. For example, if we run a program with the command./barOfStars 10
then we can access the value "10" as argv[1], and use atoi to convert this from char * to int
```
int width;

if (argc >= 2) 

  width = atoi(argv[1]);

     
```
We should put #include <stdlib.h> in our program before calling atoi().
The name atoi() comes from "ASCII to integer"
ASCII is the code that is used to convert individual characters are converted into binary and stored in the computers memory. In this code, the digit 0 is represented as 48, 1 as 49, 2 as 50, etc.
If we pass in something that isn't numeric at all to atoi, e.g. atoi("foo"), we get back the value 0.
If we pass in something that starts with a valid integer, that number is returned, and the rest is ignored—for example atoi("4evah") returns 4, and atoi("4.9999") returns 4.

If you need some more refreshers on how atoi works, go back to lab03 and go through the Ch session again.

Back to lab04

Copyright 2009, Phillip T. Conrad, CS Dept, UC Santa Barbara. Permission to copy for non-commercial, non-profit, educational purposes granted, provided appropriate credit is given; all other rights reserved.