Convert a floating point number to string in C

// C program for implementation of ftoa() 
#include <math.h> 
#include <stdio.h> 

// Reverses a string 'str' of length 'len' 
void reverse(char* str, int len) 
{ 
    int i = 0, j = len - 1, temp; 
    while (i < j) { 
        temp = str[i]; 
        str[i] = str[j]; 
        str[j] = temp; 
        i++; 
        j--; 
    } 
} 

// Converts a given integer x to string str[]. 
// d is the number of digits required in the output. 
// If d is more than the number of digits in x, 
// then 0s are added at the beginning. 
int intToStr(int x, char str[], int d) 
{ 
    int i = 0; 
    while (x) { 
        str[i++] = (x % 10) + '0'; 
        x = x / 10; 
    } 

    // If number of digits required is more, then 
    // add 0s at the beginning 
    while (i < d) 
        str[i++] = '0'; 

    reverse(str, i); 
    str[i] = '\0'; 
    return i; 
} 

// Converts a floating-point/double number to a string. 
void ftoa(float n, char* res, int afterpoint) 
{ 
    // Extract integer part 
    int ipart = (int)n; 

    // Extract floating part 
    float fpart = n - (float)ipart; 

    // convert integer part to string 
    int i = intToStr(ipart, res, 0); 

    // check for display option after point 
    if (afterpoint != 0) { 
        res[i] = '.'; // add dot 

        // Get the value of fraction part upto given no. 
        // of points after dot. The third parameter 
        // is needed to handle cases like 233.007 
        fpart = fpart * pow(10, afterpoint); 

        intToStr((int)fpart, res + i + 1, afterpoint); 
    } 
} 

// Driver program to test above function 
int main() 
{ 
    char res[20]; 
    float n = 233.007; 
    ftoa(n, res, 4); 
    printf("\"%s\"\n", res); 
    return 0; 
}