Read symbols from the keyboard and replace them with a specific pathterin in C

[emerson]

We need to scrub the line that the user turns from the keyboard and change it on a certain pathet, and then put it in the console. Can't check the condition that in the current symbol only the letters how to finish or improve the code?

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>
int checkString(const char s[]) {

unsigned char c;

while ( (c = *s) && (isalpha(c) || isblank(c))) ++s;

return *s == '\0';

}
void replacechar(char *s, char c1, char c2) {

int i = 0;

for(i = 0; s[i]; i++) {

if(s[i] == c1) {

s[i] = c2;

}

}

}
void main() {

int a;

unsigned count = 0;

printf("Enter your number: ");

while ((a = getchar()) != '~') {

// If that was in first time - first symbol is dot

if ((char) a == '.' && count == 0) printf("0.");

// If second symbol is letter than stop

if (isalpha((char) a) == 1) printf("%c", (char) a);

}

}

[amarantha]

I would do something to meet all the the requirements (and the introduction and the withdrawal and the occasional entry):

int main()
{
    for(;;)
    {
        char buf[256] = { 0 }, *o = buf;
        printf("Введите число: ");
        int c = getchar();
        if (c == '\n') break;      // Пустая строка - выход
        if (c == '.' || c == ',')  // Точка первая или нет?
            *o++ = '0';
        ungetc(c,stdin);
    int dot = 0;
    for(;;)
    {
        c = getchar();
        if (isdigit(c)) { *o++ = c; continue; } // Цифра
        if (!dot && (c == '.' || c == ','))     // Точка,
        {                          // которой еще не было
            *o++ = '.';
            dot = 1;
        } else break;
    }
    while(c != '\n') c = getchar();
    printf("Вы ввели: %s", buf);
    if (!dot && o != buf) printf(".00");  // Если точки не было,
    puts("");                             // а число было
}

}

The end of the job is when the line is empty.