Error handling exponent ("e") preceding digit - c++

Question

I'd like to create a function that checks whether a number input with an exponent such as 1.32e2, 1e3, +1.32e+2 indeed has the e in the correct position, after a number, not before it (such as e1 or .e4)
I'm a beginner so it's just trial and error at this point. This is what I have so far:
bool validate_alpha_e(string op) {
if (count_alpha(op) <= 1) {
if (count_es(op) == 1) {
//return true;
int length = op.length();
for (int i = 0; i < length; i++) {
char ch = op[i-1];
if (ch == 'e' || ch == 'E') {
if (i-1 != isdigit(i)) {
return false;
}
}
}
return true;
}

Answer 1

Worked it out. Thanks for the comments but I wasn't able to figure it out.
So I had to create 3 separate functions (see below)
First function validates for correct input before the e.
Second function validates for correct input after the e.
Third function validates that the first character is not an e.
Put all these together in a bool if statement and if it returns false then the input is not correct.
bool validate_e_after(string op) {
int length = op.length();
for (int i = 1; i < length; i++) {
char ch = op[i-1];
if (ch == 'e' || ch == 'E') {
char ch2 = op[i];
if (isdigit(ch2) || ch2 == '+' || ch2 == '-') {
return true;
}
else {
return false;
}
}
}
}
bool validate_e_before(string op) {
int length = op.length();
for (int i = 1; i < length; i++) {
char ch = op[i+1];
if (ch == 'e' || ch == 'E' && i != 0) {
char ch2 = op[i];
if (isdigit(ch2) || ch2 == '+' || ch2 == '-') {
return true;
}
else {
return false;
}
}
}
}
bool validate_ezero(string op) {
int length = op.length();
for (int i = 0; i < length; i++) {
char ch = op[i];
if (ch == 'e' or ch == 'E') {
if (i == 0) {
return false;
}
}
}
return true;