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Expressions and Statements in C

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Expression

A combination of operands and operators that produces a value is called an expression. 
c = a + b;
PartRole
a and bOperands
+Arithmetic operator
=Assignment operator
a + bExpression (evaluates to a value)
More examples: 
x * y          // arithmetic expression
x > y          // relational expression (true/false)
x && y         // logical expression
x = 5          // assignment expression — returns 5

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Statement

A statement is a complete instruction in C that performs an action. Most statements end with a semicolon (;).

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Types of Statements

Declaration Statement — creates a variable: 
int x;
Assignment Statement — assigns a value: 
x = 10;
Expression Statement — evaluates an expression: 
a + b;
x++;
Function Call Statement — calls a function: 
printf("Hello");
scanf("%d", &x);
Control Flow Statement — changes execution order: 
if (x > 0) { ... }
while (x < 10) { ... }
for (int i = 0; i < 5; i++) { ... }
Compound Statement (Block) — a group of statements enclosed in {}: 
{
    int a = 5;
    int b = 10;
    int c = a + b;
}
A block is treated as a single unit. Variables declared inside a block are local to that block.

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Key Difference

ExpressionStatement
DefinitionProduces a valuePerforms an action
Examplea + bint a = 5;
Ends withNo semicolon neededSemicolon ;