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Parsing numbers from strings is a basic but common task in many programs. Here’s how to do it in Go using the strconv package.

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Parsing Floats

The 64 parameter tells how many bits of precision to parse: 
f, _ := strconv.ParseFloat("1.234", 64)
fmt.Println(f)
// Output: 1.234

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Parsing Integers

For ParseInt, the 0 means infer the base from the string. 64 requires that the result fit in 64 bits: 
i, _ := strconv.ParseInt("123", 0, 64)
fmt.Println(i)
// Output: 123

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Hexadecimal Numbers

ParseInt recognizes hex-formatted numbers: 
d, _ := strconv.ParseInt("0x1c8", 0, 64)
fmt.Println(d)
// Output: 456

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Parsing Unsigned Integers

ParseUint is available for unsigned integers: 
u, _ := strconv.ParseUint("789", 0, 64)
fmt.Println(u)
// Output: 789

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Convenience Function: Atoi

Atoi is a convenience function for basic base-10 int parsing: 
k, _ := strconv.Atoi("135")
fmt.Println(k)
// Output: 135

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Error Handling

Parse functions return an error on bad input: 
_, e := strconv.Atoi("wat")
fmt.Println(e)
// Output: strconv.Atoi: parsing "wat": invalid syntax
Always check the error return value when parsing user input to handle invalid data gracefully.

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Parse Functions

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ParseFloat
func(s string, bitSize int) (float64, error)
Parses a floating-point number. bitSize: 32 or 64
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ParseInt
func(s string, base int, bitSize int) (int64, error)
Parses an integer. base: 0 (auto-detect), 2-36. bitSize: 0, 8, 16, 32, 64
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ParseUint
func(s string, base int, bitSize int) (uint64, error)
Parses an unsigned integer. base: 0 (auto-detect), 2-36. bitSize: 0, 8, 16, 32, 64
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Atoi
func(s string) (int, error)
Shorthand for ParseInt(s, 10, 0), converted to int

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Base Detection

When base is 0, ParseInt auto-detects the base:
Hexadecimal: 0x1c8 → 456
Octal: 0o755 → 493
Binary: 0b1010 → 10
Decimal: 123 → 123

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Number Formatting

To convert numbers to strings, use the Format functions: 
// Format integer to string
s := strconv.FormatInt(123, 10)
fmt.Println(s) // Output: "123"

// Format float to string
f := strconv.FormatFloat(3.14, 'f', 2, 64)
fmt.Println(f) // Output: "3.14"

// Shorthand for base-10 int to string
i := strconv.Itoa(456)
fmt.Println(i) // Output: "456"

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