If a random variable X follows the binomial distribution, the probability of getting k successes in n trials is given by the following probability mass function:

$f\left(k\right) \= P\left(X\=k\right)\= \left(\genfrac{}{}{0ex}{}{n}{k}\right) {\left(p\right)}^k {\left(1-p \right)}^{\left(n-k\right)}$   

for $k \= 0\,1\,2\, ..\. \, n$

where:

$\left(\genfrac{}{}{0ex}{}{n}{k}\right) \= \frac{n\!}{k\!\left(n-k\right)\!}$ 

p is probability of a successful event

k is the number of success trials

n is the number of trials

The cumulative distribution function is defined as:

$f\left(k\right) \= P\left(X\le k\right)\=\sum _{i\= 0}^{⌊k⌋}\left(\genfrac{}{}{0ex}{}{n}{i}\right) {\left(p\right)}^i {\left(1-p \right)}^{\left(n-i\right)}$   

for $k \= 0\,1\,2\, ..\. \, n$

Note that the probability function and cumulative distribution function for the binomial distribution are only defined for integer values for k and as such, there is no continual curve which can be drawn through the point.  The gray lines are only for illustrating the shape of each function over the interval.