Convert a floating point number to string in C

In C, converting a floating point number to a string is accomplished using the sprintf() function. This function works similarly to printf(), but instead of printing to the console, it writes the formatted output to a string buffer.

Syntax

int sprintf(char *str, const char *format, ...);

Parameters:

• str − Pointer to the destination string buffer
• format − Format string specifier (e.g., "%f" for float)
• ... − Variable arguments to be formatted

Example 1: Basic Float to String Conversion

The following example demonstrates converting a floating point number to a string using sprintf() −

#include <stdio.h>

int main() {
    char str[20];
    float number = 42.26;
    
    sprintf(str, "%f", number);
    printf("Original number: %.2f<br>", number);
    printf("Converted string: %s<br>", str);
    
    return 0;
}

Original number: 42.26
Converted string: 42.260002

Example 2: Controlling Decimal Precision

You can control the number of decimal places using format specifiers −

#include <stdio.h>

int main() {
    char str[20];
    float number = 123.456789;
    
    sprintf(str, "%.2f", number);  // 2 decimal places
    printf("With 2 decimals: %s<br>", str);
    
    sprintf(str, "%.4f", number);  // 4 decimal places
    printf("With 4 decimals: %s<br>", str);
    
    return 0;
}

With 2 decimals: 123.46
With 4 decimals: 123.4568

Example 3: User Input Conversion

This example takes user input and converts the floating point number to string format −

#include <stdio.h>

int main() {
    char str[50];
    float number;
    
    printf("Enter a floating point number: ");
    scanf("%f", &number);
    
    sprintf(str, "%.3f", number);
    printf("You entered: %s<br>", str);
    
    return 0;
}

Enter a floating point number: 46.3258
You entered: 46.326

Key Points

• Ensure the destination buffer is large enough to hold the converted string
• Use format specifiers like %.2f to control decimal precision
• sprintf() returns the number of characters written (excluding null terminator)

Conclusion

Converting floating point numbers to strings in C is efficiently handled by sprintf(). This function provides precise control over formatting and is essential for string manipulation in C programming.