c,char,printf,decimal,ascii , Conversion from char to int and printing the decimal value

## Question:

Tag: c,char,printf,decimal,ascii
``````char str[20];
printf("Enter anything\n");
scanf("%s",str);
for(int i = 0 ; i<strlen(str) ; i++)
{
if( isdigit(str[i]))
printf("%d",(int)str[i]);
}
``````

I tried with the above code but the output is in ASCII values of the numbers rather then actual numbers. Like , input: "0" output: "48".

When I try `(int)(str[i]-'0');` instead of `(int)str[i]);` , I get the correct answer but I don't understand why it's correct.

There are two ways you could modify your code to do what you want. The first, would be to change the printf to print the character representation rather than the integer representation of the value.

``````printf("%c", str[i]);
``````

Will print "0" given the in put of the string "0" from the keyboard.

The other one, which you mentioned in your question is:

``````printf("%d", (int)(str[i]-'0'));
``````

The reason you get the correct answer here has to deal with how the computer stores values. When you type a "0", it doesn't actually store the value 0. It stores instead the ASCII representation of a character we call "0". That value happens to be the integer 48. 49 represents the character "1" and so forth.

Why? Well think about representing the character "M" or perhaps "#". What should represent those? ASCII is a known representation of 256 characters (roughly) since that's the total number of values we can store in 1 byte. So, "M" is 77 and "#" is 35.

The reason str[i] - '0' works has to do with the way C/C++ handles characters ('0' is a character). The character 'M' is exactly equivalent to the value 77. So these two lines would be equivalent:

``````str[i] - '0'
``````

is the same as

``````str[i] - 65
``````

Because I enter a "1" (string) which is represented in the binary as a 66, I subtract 65 and I get 1, the value. When I ask printf to display the integer value (%d) of my result

``````printf("%d", (int)(str[i] - '0'));
``````

it prints "1" because 66 - 65 is 1. Or '1' - '0' is 1.

Just remember that any time you're looking at a string or a character you aren't looking at the digital or binary representation of a value, you're looking at the ASCII representation of that value.

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