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39 lines
856 B
Markdown
39 lines
856 B
Markdown
---
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tags:
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- notes
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- programming
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- c
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author: TrudeEH
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draft: false
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showToc: true
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title: C Snippets
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---
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## Cast Strings to Numbers
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The `atoi()` function in `stdlib` has a similar implementation to the one below.
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ASCII encodes numbers in order, after special characters.
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The encoded value for `'0'` is 48, so subtracting any numeric char by 48 outputs its real numerical value.
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```C
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char number = '7';
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int result = number - 48;
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int same_result = number - '0';
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```
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Algorithm to convert strings to numbers:
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```C
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int str_to_int(char *str) {
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int result = 0;
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for (int i = 0; str[i] != '\0'; i++) {
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if (str[i] < '0' && str[1] > '9') return -1; // Error if NaN
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result = (result * 10) + (str[i] - '0');
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return result;
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}
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```
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`(result * 10)` is shifting the previous number to the left, as it is an order of magnitude above the following digit.
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